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[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 91.12%. Comparing base (c8defc7) to head (b82f843). :warning: Report is 79 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1617   +/-   ##
=======================================
  Coverage   91.12%   91.12%           
=======================================
  Files          37       37           
  Lines       17123    17123           
=======================================
  Hits        15603    15603           
  Misses       1520     1520           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[djc]

I definitely don't want to take a 1.81 MSRV bump. We could make this an opt-in feature core-error, though?