Add deterministic Rust realization adapter

[aryamantodkar]

Summary

• add the premove-itn-core Rust crate and pin text-processing-rs v0.3.0
• expose PyO3 functions for forced span realization, the upstream sentence baseline, and TN
• route configured English ITN kinds directly to their upstream parsers
• add the strict local DIGIT_SEQUENCE extension with leading-zero and repetition support
• keep Rust tests in a separate test file and document the deterministic routes

Why

The contextual model must select spans and classes without generating replacement text. This adapter establishes the deterministic boundary that converts an accepted source span through one explicitly selected realizer.

Invariant

A supported class calls only its configured deterministic parser. Unknown classes return an error, rejected spans return no replacement, and the local digit-sequence parser rejects incomplete or unknown input.

Without this boundary, the later classifier could depend on the upstream fixed-priority sentence dispatcher or construct normalized values itself, which would hide class errors and weaken fail-closed behavior.

Supported routes

• upstream: CARDINAL, DATE, DECIMAL, ELECTRONIC, MONEY, MEASUREMENT, ORDINAL, PUNCTUATION, PHONE, TIME, WHITELIST, WORD
• local extension: DIGIT_SEQUENCE

FRACTION is not routed because the pinned crate exposes it under tn::en, not itn::en; that parser runs in the opposite direction.

Validation

• cargo fmt --check
• cargo test --locked — 15 passed
• cargo clippy --locked --all-targets -- -D warnings
• uv run pytest — 1 passed
• uv run ruff check .
• uv build