Prepare semantic tokens to include syntax highlighting

[magic-akari]

Summary

Pyrefly's semantic pipeline currently models only identifier-level tokens. Future support for a full semantic stream therefore requires a syntax-token source covering keywords, comments, strings, numbers, and operators.

This change introduces a lightweight syntax path derived from Ruff's parse results and configures the LSP encoder to split multiline ranges into line-local tokens. To ensure the new path remains unadvertised, this server capability is gated to clients that already augment syntax tokens.

This enables proper representation of triple-quoted strings and preserves current semantic-overlay behavior during the gated rollout.

Test Plan

• python3 test.py --no-test --no-conformance --no-jsonschema
• cargo test

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