1.8.0 — more decoders

The Python package and the Rust crate both at 1.8.0, "more decoders": four decoders the field
compares against, each ported from its authors' code and held to it shot for shot
(tools/decoder_check.py, run in CI). API additions only.

Added

• BP+LSD (BpLsd on a model, BpLsdDecoder on a check matrix with ldpc's arguments;
  Rust BpLsd, BpLsdDecoder, LsdOptions): belief propagation, then localized statistics
  decoding (Hillmann et al., 2024), LSD-0, LSD-E and LSD-CS. Corrections equal to ldpc
  2.4.1's on every shot checked; the only differences possible are where ldpc's own order
  is not reproducible (equal keys in a long std::sort, or several clusters merged at once,
  which it orders by hashed pointers), and those shots are reported as ties. Each cluster's
  faults iterate in ldpc's tsl::robin_set order, which is reproduced. 0.6 of ldpc's time
  on the gross code.
• Relay-BP (RelayBp, RelayBpDecoder; Rust RelayBp, RelayBpDecoder,
  RelayOptions): min-sum BP with memory, run in legs of disordered memory strengths (Müller
  et al., IBM, 2025). Identical to IBM's relay_bp 0.2.2 on every shot (correction,
  convergence and iteration count), for explicit strengths and for a seed: its random
  strengths come from rand 0.8's generator, reproduced without the dependency. A model's
  shot k draws from the seed and k, so results do not depend on the thread count.
• Colour-code matching (ColorMatching; Rust ColorMatching): Chromobius's Möbius
  construction (Gidney and Jones, 2023) on this package's matcher. The Möbius matching weighs
  the same as Chromobius 1.1.1's on every shot checked, and predictions differ only between
  equally light matchings. 0.74 of Chromobius's time at d = 7.
• A search decoder (SearchDecoder; Rust SearchDecoder, SearchOptions,
  DetectorOrder): Tesseract's A* for the most likely error (Beni, Higgott and Shutty,
  Google, 2025), for any model. The faults it finds are Tesseract's, fault for fault, on the
  same platform (its ties are broken as the platform's C++ library breaks them). With no
  beam, no queue bound and revisits allowed it is exact.
• Colour annotations: CssCode.memory_circuit(..., annotate_colors=True) (Rust
  memory_circuit_with_colors) gives each detector Chromobius's 4th coordinate;
  Circuit.generated("color_code:memory_xyz", ..., annotate_colors=True) (Rust
  generated_with_colors) flattens Stim's colour code and annotates it as Chromobius's
  authors do.
• The four in stabilizer_qec.sinter ("bplsd", "relay_bp", "color_matching",
  "search") and in stabilizer-qec decode --decoder; fuzzed with Hypothesis and
  fingerprinted; benchmarked against their references; tutorial 04 compares every decoder on a
  colour code and the gross code.

The Rust crate stabilizer_qec 1.8.0 (tag crate-v1.8.0) has the same additions.