Harden quality gates and finalize mutation coverage

[vitormattos]

Summary

• fold the pending PNG wrapper/runtime work from fix/infection-uncovered-main into this branch before layering the newer hardening changes
• tighten repository quality gates across PHPUnit, Psalm, workflows, duplication checks, and Infection
• finish the remaining parser/exporter/PNG hardening and expand regression coverage, including provider-based test cleanup where it reduced duplication safely

Validation

• composer test:unit
• composer run test:integration
• composer phpmd
• composer lint
• composer run mutation:test

Notes

• the branch was rebased onto fix/infection-uncovered-main intentionally so the previously skipped PNG changes are not lost or reintroduced later as conflicts
• final local validation on this branch finished with Infection 1611/1611 killed and no errors, uncovered mutants, or timeouts