Bump MSRV to 1.86 (and codspeed)

[AdamGS]

Since we're on the 2024 edition, bumping the msrv is no longer considered a breaking change because of this change. 81% of crates.io traffic comes from 1.86 or later, compared to 89% that use 1.85 or later, so we don't lose a huge amount the potential ecosystem.
This also unblocks codspeed with much better capabilities at "seeing" inlined code, which is very valuable here.

[codspeed-hq]

CodSpeed Performance Report

Merging #149 will improve performances by ×2

_{Comparing adamg/bump-msrv-divan (9cae91f) with develop (1f3875d)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

⚡ 1 improvement
✅ 31 untouched

Benchmarks breakdown

	Mode	Benchmark	BASE	HEAD	Change
⚡	WallTime	compress-twobytes	2 ns	1 ns	×2

[a10y]

Yea this is probably fine. But also, I'm assuming there's a way to configure which toolchain codspeed uses?

[AdamGS]

Its possible (RUSTUP_TOOLCHAIN) but it seems like just more complexity. We can just hold this until 1.86 becomes as popular as 1.85 is now (taken from the bottom of this page)/is a year old or some other popularity metric.