test: move tests to integration tests

[Boshen]

Moves parser and lexer coverage into Cargo integration targets, so the crate is exercised through its public API.

Validated with cargo test -p oxc-graphql-parser.

[codspeed-hq]

Merging this PR will not alter performance

✅ 5 untouched benchmarks
⏩ 5 skipped benchmarks¹

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_{Comparing codex/move-tests-to-integration (1d44ad5) with main (ffc3b99)}

Footnotes

1. 5 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩