find: Fix convert_arg_to_comparable_value() function parsing unexpected characters.

[hanbings]

convert_arg_to_comparable_value() as mentioned in #355 (comment) parses some strange characters.

The original regular expression was ([+-]?)(\d+)$ , which did a partial match and only included 1%2 of 2 as part of the match.
After adding the ^ limiter (^([+-]?)(\d+)$), the expression can be restricted to only match + - or 0-9.

[codecov]

Codecov Report

Attention: Patch coverage is 94.11765% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 58.88%. Comparing base (baa09ba) to head (c0b8cd0).

Files	Patch %	Lines
src/find/matchers/mod.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
+ Coverage   58.34%   58.88%   +0.53%     
==========================================
  Files          30       30              
  Lines        3815     3831      +16     
  Branches      860      860              
==========================================
+ Hits         2226     2256      +30     
+ Misses       1257     1254       -3     
+ Partials      332      321      -11     

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[sylvestre]

please add integration tests too to trigger the error and make sure we are handling it correctly

[hanbings]

Thanks.
I added an command test for the -a/c/mtime directive in find_cmd_tests.rs.

But it may be that Codecov does not detect the diff because the PR only fixes regular expressions, so the coverage changes cannot be seen in the Codecov report.