Bump to v0.3.0

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

v0.2.0: SIMD-accelerated XML parser for Python

Tag name interning, lazy ElementList, zero-copy parse, upstream API integration. 2-42x faster than lxml across parse/XPath/traversal benchmarks. 191 tests, pyright clean, ruff clean.

Fix release CI: replace deprecated macos-13 with macos-latest

macos-13 runner is no longer supported on GitHub Actions.
Use macos-latest for both x86_64 (cross-compiled) and aarch64 (native).

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>