2.0.0

A major release: critical correctness fixes, a rework of the library's concurrency
story, removal of APIs that didn't make sense, and a batch of new generators. If you are
coming from 1.x, build against 1.3.0 first — it deprecates everything 2.0 removes, with
messages naming the replacements.

Concurrency: RandomGenerator no longer requires Sendable

Generators are ordinary values, confined to the isolation domain where they are built
and run:

• The protocol requires neither Sendable nor Element: Sendable. Conformers may hold
  non-Sendable state and produce non-Sendable values.
• Transform closures (map, flatMap, filter, retry, tryMap, ...) are plain
  closures — they can capture anything the surrounding context can.
• Leaf generators (IntGenerator, FloatGenerator, BoolGenerator, Always,
  Character, UnicodeScalar, the seeded RNGs, and all ready-made generators) declare
  Sendable explicitly, and closure-free combinators (Array, Collect, Concat,
  Dictionary, Element, Frequency, OneOf, OrNil, Print, Shuffled, Tuple,
  Zip, ...) propagate it conditionally — so leaf-only compositions remain shareable.
• RemoveDuplicates drops its lock and @unchecked Sendable; the compiler now enforces
  its single-domain confinement.
• AttemptBounded.FallbackStrategy is no longer Sendable (it carries a closure).

Migration: pipelines containing closures are no longer Sendable. Move one into a
Task and region isolation checks the transfer; to use a pipeline from several tasks,
build one per task.

Fixed

• AnyRandomGenerator never advanced the caller's RNG — erased generators (including
  the character presets) replayed the same value forever under a seeded RNG. Seeded
  sequences involving erased generators change with this fix.
• Zip(...).map { a, b, c in } compiles again on Swift 6.3 via a pack-argument overload.
• compactMap/retryMap could crash on a force-unwrap when the attempt budget was
  exhausted; they now produce Optional (nil on exhaustion). retryThrowing produces
  Result (the last failure on exhaustion), runs its transform once per candidate, and
  no longer backstops with fatalError.
• uiColor(alpha:)/swiftUIColor(alpha:) silently ignored their alpha parameter; the
  parameter is removed and the generator's init(alpha:) visibly governs.
• UnicodeScalar/Character generation over ranges spanning the surrogate gap
  (U+D800–DFFF) no longer biases toward the lower bound or traps; the gap is skipped
  uniformly.
• Frequency no longer materializes a sum-of-all-weights array on every run (cumulative
  bounds + one draw), and fails fast with clear preconditions on empty or all-zero
  distributions.
• AttemptBounded counts the initial run toward maxAttempts (previously
  maxAttempts: 3 ran the upstream up to 4 times); maxAttempts must be ≥ 1.
• IntGenerator(in: 0..<0) traps with a clear message instead of a confusing
  ClosedRange precondition.
• The package declared iOS 13 but could not compile for iOS at all (Zip's parameter
  packs require the iOS 17 runtime). Platforms are now honestly declared —
  iOS 13 / macOS 10.15 / tvOS 13 / watchOS 6 — with only Zip and its operators gated
  behind @available(macOS 14, iOS 17, tvOS 17, watchOS 10).
• IPAddressGenerator imports Foundation explicitly.

Added

• RandomGenerators.Bernoulli / .bool(probability:) — biased coin.
• orNil(probability:) — produce nil with a given probability.
• RandomGenerators.Normal (Box–Muller) and RandomGenerators.Exponential
  distributions, with .normal(mean:standardDeviation:) / .exponential(rate:) sugar.
• RandomGenerators.oneOf(...) — uniform pick across 2–4 generators of different
  concrete types sharing an element type.
• RandomGenerators.string(of:count:) and characterGen.string(count:).
• Seeded RNGs: Xoshiro256 (xoshiro256++), SplitMix64, PCG (independent streams via
  sequence:).
• Dice(sides:) with d4/d6/d8/d10/d12/d20/d100 presets.
• Dot-syntax statics: .int(in:), .float(in:), .bool.
• RandomGenerators.sudoku(difficulty:) convenience.
• DocC catalogs for both modules and the swift-docc-plugin.
• A runnable example target exercising the whole API.

Changed (breaking)

• BoolRandomGenerator is renamed BoolGenerator (deprecated typealias retained).
• compactMap/retryMap produce Output?; retryThrowing produces
  Result<Output, Error>.
• Frequency is constructed via RandomGenerators.frequency(_:); the receiver-ignoring
  instance method is removed.
• UnicodeScalar and Character are standalone generators constructed from a range;
  the combinator forms (whose upstream was ignored) are removed.

Removed

• ZipArrayGenerator, zipAll(), zipGenerators(...) — exact duplicates of Collect;
  use [generators].collect().
• gen.always(_:), gen.colorGenerator(alpha:) — receiver-ignoring factories; construct
  Always(_:) / ColorGenerator(alpha:) directly.
• CreditCardGenerator.Generated — use Element.