feat: Change to use core::error::Error

[sorairolake]

Change to use core::error::Error instead of std::error::Error. The MSRV is bumped up to 1.81.0 by this change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.7%. Comparing base (4a74924) to head (df0491c).
Report is 44 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #706     +/-   ##
=======================================
- Coverage   97.8%   97.7%   -0.1%     
=======================================
  Files         81      83      +2     
  Lines       9378    8974    -404     
=======================================
- Hits        9169    8767    -402     
+ Misses       209     207      -2     

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[jhpratt]

This violates the MSRV policy in the README. Additionally, I am very deliberate about bumping MSRV and track a number of features to ensure that I'm not increasing it for only a single thing.

[sorairolake]

I think this will no longer be a violation of the MSRV policy once Rust 1.83 is released. So I think this can be kept as draft pull request.

[jhpratt]

I do not intend to bump the MSRV the moment 1.83 is out. I will batch a number of changes together and do it all at once, not piecemeal. That's not to mention the countless changes made in this PR for unclear reasons.

[sorairolake]

That's not to mention the countless changes made in this PR for unclear reasons.

@jhpratt This is because the CI will not pass unless apply cargo fmt to unchanged files too. This is unrelated to this change, so I separated it out as df0491c.