`no_std` support

[polarathene]

I do not personally require this, I'm just opening a tracking issue as the current README entry was a tad vague on the why:

eyre/README.md

Lines 178 to 182 in dbaf9ed

	## No-std support
	No-std support was removed in 2020 in [commit 608a16a] due to unaddressed upstream breakages.
	[commit 608a16a]:
	https://github.com/eyre-rs/eyre/pull/29/commits/608a16aa2c2c27eca6c88001cc94c6973c18f1d5

Actual context for removal appears to be covered here:

• Update documentation on no_std support. #111 (comment)
• no_std blockers #199 (comment)

Which seems to have been resolved from Rust 1.81 with core::error::Error landing? (and thus by default for new projects created with the current 2024 edition (from Rust 1.85))

As per the discussion link, the desire was to wait a few release cycles of Rust (which 1.85 should be sufficient?). I assume that requires a notable MSRV bump though? Cargo.toml may need to update:

eyre/Cargo.toml

Line 10 in dbaf9ed

edition = "2018"

eyre/Cargo.toml

Line 14 in dbaf9ed

rust-version = "1.65.0"

---

Contribution of a PR was encouraged should anyone want to bring no_std support back.