v0.3.2

Bump v0.3.2: default validate_strings to true for Jason parity

Jason's decoder always validates UTF-8 (its parser matches ::utf8
codepoints and rejects control bytes). The v0.3.1 default of
validate_strings: false broke the Jason-parity guarantee. Now defaults
to true across Elixir, Rust Default impl, and NIF option extraction.

- Update docs, ARCHITECTURE.md, and CHANGELOG
- Add CHANGELOG.md to hex package files
- Move 10 invalid-UTF-8 JSONTestSuite i_* fixtures to @implementation_rejects
- Add test for opt-out via validate_strings: false
- 421 tests, 0 failures

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>