blockchainkit 0.2.0

The package is aligned with its kit-family siblings, and every subpackage now
follows its field through at least 15 breakthroughs, each with its own
experiment.

Added

• Tutorials across subpackages, every line run by the doctest build: Life of
  a payment, Nonces everywhere, Hashes everywhere and Who do you
  trust?.
• Exercise pages, one per subpackage, with 40 worked solutions in collapsed
  boxes, each run by the doctest build. They replace the single solutions page.
• A "Teaching vs production" note on every history entry that adapts a
  deployed protocol, naming the difference.
• README figures, regenerated by docs/make_readme_figure.py and
  docs/make_readme_subpackage_figures.py.
• Execution history: 16 breakthroughs, each with its own gallery example,
  from reverse Polish notation (1924-1957) to the BeautyChain overflow
  (2018). New APIs: execute(..., arguments=...), the Forth words OVER and
  ROT, REVERT, and the shared STACK_EFFECTS table; validate_program;
  assemble (labels); to_rpn and compile_expression; verify_bytecode
  and VerificationResult; run_turing_machine, enumerate_machines and
  busy_beaver (reproducing S(2) = 6); Bitcoin-style Script with
  verify_script, p2pkh_locking/p2pkh_unlocking and htlc_locking
  (OP_CHECKLOCKTIMEVERIFY); the contracts vending_machine and
  batch_transfer (BEC overflow, with a SafeMath option); drain_bank
  (DAO reentrancy); and the plot plot_stack_height.
• Network history: 17 breakthroughs, each with its own gallery example, from
  Erdős-Rényi random graphs (1959) to Dandelion (2017). New APIs: Graph,
  erdos_renyi, ring_lattice, watts_strogatz, barabasi_albert and
  complete_graph; lamport_timestamps, vector_timestamps,
  happened_before and concurrent; spread_rumor (push, pull, push-pull)
  and pittel_rounds; reliable_broadcast (Bracha); ReplicatedRegister
  (CAP); KademliaNetwork, xor_distance and node_id; AddressManager
  and eclipse_probability; relay_cost, compact_block_relay and
  short_id; fork_rate and simulate_fork_rate; first_spy_precision;
  SimulatedNetwork.from_graph and SimulatedNetwork.messages_sent; the
  plots plot_graph, plot_space_time and plot_rumor_spread; and the
  COMPACT_BLOCK_DOMAIN constant.
• Consensus history: 17 breakthroughs, each with its own gallery example,
  from the gambler's ruin (1656) to Casper FFG (2017). New APIs:
  oral_messages (Byzantine generals); ben_or (randomized consensus, also
  used to show the FLP adversary); view_changes (partial synchrony);
  modular_square_root (Dwork-Naor pricing); pbft_round and
  quorum_size; attacker_success_probability (whitepaper section 11, checked
  against its table); retarget and simulate_difficulty; ghost_tip and
  subtree_work; selfish_mining_revenue, selfish_mining_threshold and
  simulate_selfish_mining; fork_voting_payoffs (nothing at stake);
  sortition; and FinalityGadget (Casper FFG with slashing detection).
• Structures history: 15 breakthroughs, each with its own gallery example,
  from double-entry bookkeeping (1494) to Merkle mountain ranges (2016). New
  APIs: Ledger.total_supply; BloomFilter; hash_chain and
  verify_one_time_password; BlockHeader, Block.to_header() and
  verify_header_chain for light clients; bitcoin_merkle_root (Bitcoin's
  duplicated-leaf convention, for CVE-2012-2459); MerkleTree.consistency_proof
  and verify_consistency (RFC 6962/9162); UTXOSet, UTXOTransaction,
  OutPoint and Coin; Transaction.unsigned_id (SegWit-style);
  SparseMerkleTree with membership and non-membership proofs; and
  MerkleMountainRange.
• Cryptography history: 22 breakthroughs, each with its own gallery example,
  from the one-time pad (1917-1949) to MuSig (2018). New APIs behind them:
  one_time_pad/xor_bytes; baby_step_giant_step and pohlig_hellman;
  merkle_puzzles/solve_puzzle; lamport_keypair/lamport_sign/
  lamport_verify; find_collision/truncated_hash; a readable
  Merkle-Damgard SHA-256 (merkle_damgard_sha256, sha256_compress,
  sha256_padding) with length_extension; naive_mac and hmac_sha256;
  pedersen_commit/pedersen_generators; feldman_split/feldman_verify;
  TEACHING_GROUP, a 62-bit safe-prime group; simulate_transcript;
  deterministic_nonce (RFC 6979, checked against the RFC's vectors); and
  musig_coefficients/aggregate_public_keys/musig_sign.
• visualizers/ in every subpackage (Matplotlib, imported explicitly; plain
  import blockchainkit still loads only the standard library):
  plot_curve_points, plot_hamming_distances, plot_merkle_tree,
  plot_proof_trace, plot_block_tree, plot_mining_trials,
  plot_stake_shares, plot_gossip_timeline, plot_execution_trace.
  Matplotlib and NumPy are now runtime dependencies; the examples extra is
  gone.
• execute(..., trace=True) records a TraceStep after every instruction,
  following jumps; a failed run carries its partial trace in VMError.trace.
  execute(..., gas_costs=...) prices opcodes individually (each at least 1).
• MerkleTree.levels, MerkleTree.leaf_count, and trace_proof, which
  returns a MerkleTrace of ProofSteps, even for a proof that fails.
• Blockchain.blocks, tips(), work_at() and state_at() to inspect
  side forks.
• enumerate_points lists every point of a small curve.

Changed

• The documentation follows the kit-family structure: generated hub pages per
  subpackage, per-subpackage API pages, a history/ directory with one
  breakthroughs page per subpackage (each entry with its own References:
  line and minigallery), an examples index, tutorials (the guided course and
  solutions), and JupyterLite launch buttons. Examples moved to
  examples/<subpackage>/<topic>/. The committed per-example notebooks and
  their sync scripts are replaced by sphinx-gallery downloads and a single
  notebooks/quickstart.ipynb.
• The package uses the kit-family layout: one subpackage per domain with
  core/, systems/, utils/ and tests/, shared validation in
  _validation.py, and every consensus-relevant constant in constants.py.
  Public bk.<subpackage>.<name> imports are unchanged.
• A wrong argument type (bool, float, string) now raises TypeError; an
  out-of-range integer still raises ValueError. multiply reports the two
  cases separately.
• Mining varies only the header nonce: Block.merkle_root and Block.hash
  are cached, and Block.header(nonce=...) builds a candidate header without
  rebuilding the Merkle tree. Mining a 20-transaction block is about 59 times
  faster per attempt (2 µs instead of 118 µs).
• verify skips the subgroup-membership multiplications when Hasse's bound
  proves the cofactor is 1 (new Curve.cofactor_is_one), halving the cost of
  verification on secp256k1.
• Ledger, Blockchain, MerkleTree and SimulatedNetwork have readable
  reprs.

Fixed

• Transaction rejects a signature that is not a SchnorrSignature;
  before, the block hash raised AttributeError later.
• execute raises VMError, not TypeError, for a non-string opcode.
• Curve accepts secp256k1's field prime and group order only in their own
  roles; swapping them no longer skips the primality check.
• A receive callback that raises no longer leaves the payload marked seen.
• eventual_catch_up rejects non-numeric fractions, and StakeSampler and
  SimulatedNetwork reject non-integer seeds.