v0.3.0

Adds a sixth first-party port for Rust. No algorithm changes: every port
still produces byte-identical output on the shared fixture suite.

New port: smooth-reading (Rust, crates.io)

• Std only, zero runtime dependencies, #![forbid(unsafe_code)], edition
  2024, MSRV 1.85 (the edition floor). Rust's standard library has no Unicode general-category
  lookup, so the crate ships a generated code-point range table
  (rust/src/unicode_data.rs, from the Unicode Character Database) and a
  hand-written scanner that mirrors the Python port: the spec regex, the
  no-space-script run rule and the UAX #29 grapheme approximation (Hangul
  jamo composition, Indic conjunct linking, combining marks, ZWJ, CR+LF).
• tokenize returns borrowed Token<'a> values (Word / Separator)
  that slice the input without copying; to_html, to_markdown,
  fixation_length, escape_html, a clamping Options builder and
  HtmlOptions.
• A Segmenter trait with the default SpecSegmenter, so an application can
  plug in an ICU word breaker (for example icu_segmenter) for dictionary
  based Chinese, Japanese and Thai breaks without touching the algorithm.
• A smooth-reading command (cargo install smooth-reading) with the same
  flags as the Python CLI, which gains --version in this release.

Release engineering

• ci.yml builds and tests the crate on the 1.85 floor and on stable (fmt,
  clippy, doc, publish dry-run); release.yml verifies the crate version and
  publishes to crates.io with the CARGO_REGISTRY_TOKEN secret, skipping
  versions that already exist. rust/Cargo.lock is committed and every
  cargo invocation in CI runs --locked.