chore: update ada to 4.0.0

[anonrig]

Summary

• Update bundled Ada single-header files to v4.0.0.
• Bump crate version to 4.0.0 and README external-link example to version = "4".

Release: https://github.com/ada-url/ada/releases/tag/v4.0.0

Made with Cursor

[codspeed]

Merging this PR will improve performance by 52.58%

⚡ 7 improved benchmarks
✅ 9 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	ada_url	12 µs	3.7 µs	×3.2
⚡	Simulation	ada_url	205.2 µs	124.5 µs	+64.78%
⚡	Simulation	ada_url	1,338.1 µs	830.7 µs	+61.08%
⚡	Simulation	ada_url	16.7 µs	12.7 µs	+31.55%
⚡	Simulation	ada_url	18.1 µs	14.4 µs	+26.03%
⚡	Simulation	ada_url_parse	195.1 ms	165.6 ms	+17.82%
⚡	Simulation	ada_url	5.6 ms	4.8 ms	+15.1%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing chore/update-ada-4.0.0 (6f0b295) with main (29cd11b)}