Add packed glyph outline codecs

[kostyafarber]

Summary

• add strict Rust and TypeScript codecs for shift.glyph-outline.v1
• define the normative framing and validation specification
• share golden vectors between both implementations and cover malformed input and canonical re-encoding
• include a Rust codec benchmark example

Scope

This PR intentionally contains only the standalone shift-glyph-codec crate, the DOM-free @shift/glyph-codec TypeScript package, their shared fixtures/specification, and required workspace metadata.

It does not integrate the codec with the editor, renderer, workspace protocol, NAPI bridge, shift-wire, preview cache, or persistence.

shift.glyph-outline.v1 remains derived, flattened f32 rendering geometry. It is distinct from the future canonical, lossless shift.glyph-layer.v1 authored-storage format.

Validation

• full pre-commit suite
• cargo test --workspace
• cargo clippy -p shift-glyph-codec --all-targets -- -D warnings
• pnpm typecheck
• pnpm lint:check
• pnpm --filter @shift/glyph-codec test
• pnpm format:check