feat: constify mul*

[DaniPopes]

Requires bumping MSRV to 1.83

[codspeed-hq]

CodSpeed Performance Report

Merging #449 will degrade performances by 19.31%

_{Comparing DaniPopes:const-mul (f5fb253) with main (a47b1b0)}

Summary

⚡ 2 improvements
❌ 6 regressions
✅ 371 untouched

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	log/128	8.8 ms	7.7 ms	+13.34%
❌	log/192	11.8 ms	13.5 ms	-12.4%
⚡	overflowing_pow/128	534.9 µs	462.8 µs	+15.59%
❌	overflowing_pow/192	1.1 ms	1.4 ms	-19.31%
❌	overflowing_pow/256	2 ms	2.3 ms	-14.65%
❌	overflowing_pow/384	4.5 ms	5.1 ms	-11.82%
❌	root/127/192/192	15.7 ms	17.9 ms	-12.56%
❌	root/127/256/256	11.9 ms	13.2 ms	-10.15%

[prestwich]

closing as stale. can reopen if we want to