ci: use edition 2024 merged doctests under wasm & valgrind

[davidhewitt]

This is an experiment to see if wasm and valgrind jobs can run faster if we update to use merged doctests. If successful, we could instead consider MSRV bump to 1.85

[codspeed]

Merging this PR will degrade performance by 8.95%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
❌ 3 regressed benchmarks
✅ 137 untouched benchmarks
⏩ 6 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	into_u128_small	820.5 ns	1,041.4 ns	-21.21%
❌	into_u128_zero	816 ns	981.3 ns	-16.84%
❌	extract_bigint_small	1.5 µs	1.6 µs	-10.2%
⚡	into_biguint_small	1.5 µs	1.3 µs	+16.79%

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 davidhewitt:merged-wasm-doctests (d7dc6dd) with main (ff1316b)}

Footnotes

1. 6 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. ↩

[davidhewitt]

I'm playing around with the full version bump to 1.85 & edition 2024 to see what gains we get. Taking a bit of work to run the experiment, but initial results locally suggest it might net some decent wins.