✨ feat(fuzz): check standalone IDNA invariants

[gaborbernat]

The standalone IDNA target called the shared conversion core without checking its result. Add the ASCII and repeat-conversion properties from #1010, plus canonical Punycode and UTS #46 mapping checks.

Check the NFC quick-path implication against full normalization. Preserve relaxed URL handling and skip repeat conversion when expansion exceeds the wrapper input limit.

[codspeed]

Merging this PR will degrade performance by 24.94%

❌ 1 regressed benchmark
✅ 580 untouched benchmarks
⏩ 32 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	test_feature[shadow-slot-comments]	83.7 µs	111.5 µs	-24.94%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing gaborbernat:feat/idna-standalone-properties-1010 (93a7334) with main (2c0fdb7)}

Footnotes

1. 32 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. ↩