chore: add OnceLock re-export with no_std support

[DaniPopes]

Same as alloy_primitives::map that uses hashbrown, here we use once_cell::race::OnceBox for no_std OnceLock, while preferring std::sync::OnceLock.

[codspeed-hq]

CodSpeed Performance Report

Merging #2787 will degrade performances by 3.11%

_{Comparing DaniPopes:refactor-oncebox (e92699c) with main (9c0a3d2)}

Summary

❌ 1 regressions
✅ 170 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	transact_1000tx_commit_inner_every_40	2 ms	2.1 ms	-3.11%

[DaniPopes]

Small regressions look like allocator/inlining noise