refactor: use core error

[XuJiandong]

It doesn't require std. This feature is introduced since Rust 1.81.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 84.90%. Comparing base (f24752b) to head (cc53818).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/core/error.rs	0.00%	2 Missing ⚠️
src/serde/error.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #44      +/-   ##
==========================================
+ Coverage   84.69%   84.90%   +0.21%     
==========================================
  Files          11       11              
  Lines        1953     1948       -5     
==========================================
  Hits         1654     1654              
+ Misses        299      294       -5     

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[quininer]

Thank you!