chore: release v4.2.0

[Boshen]

🤖 New release

• oxc_sourcemap: 4.1.6 -> 4.2.0 (✓ API compatible changes)

Changelog

4.2.0 - 2025-09-26

Added

• reduce peak memory usage with .shrink_to_fit() (#172)

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This PR was generated with release-plz.

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[codspeed-hq]

CodSpeed Performance Report

Merging #173 will degrade performances by 1.01%

_{Comparing release-plz-2025-09-26T18-13-24Z (4f8992e) with main (ffc7e78)}

Summary

⚡ 2 improvements
❌ 1 regression
✅ 2 untouched

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	from_json_string	16.9 µs	16.7 µs	+1.4%
⚡	generate_lookup_table	1.3 µs	1.3 µs	+2.3%
❌	to_json	5.7 µs	5.8 µs	-1.01%