feat: add hexDecode transformation

[tty2]

This PR add a simple implementation of hexDecode function.
Changes are based on std lib.
Related to the issue #1253.

Json test cases were edited. At first glance it looks incorrect. This one. Look this comment.
If you have any doubts or can explain why this test case has this output, please reject the PR and let me know why this test case is valid.

• My code includes positive and negative tests.
• I have an appropriate description with correct grammar.
• I have read Contribution guidelines, maintainers note and Quality standard.
• My code is properly linted and passes pre-commit tests.

[fzipi]

It is taking a nice shape.

Can you extend the json test cases with negative tests?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.77%. Comparing base (df87141) to head (774e8a7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1275      +/-   ##
==========================================
+ Coverage   81.76%   81.77%   +0.01%     
==========================================
  Files         169      170       +1     
  Lines        9770     9777       +7     
==========================================
+ Hits         7988     7995       +7     
  Misses       1533     1533              
  Partials      249      249              

Flag	Coverage Δ
coraza.rule.case_sensitive_args_keys	81.73% <100.00%> (+0.01%)	⬆️
coraza.rule.multiphase_valuation	81.77% <100.00%> (+0.01%)	⬆️
coraza.rule.no_regex_multiline	81.71% <100.00%> (+0.01%)	⬆️
default	81.77% <100.00%> (+0.01%)	⬆️
examples+	16.54% <14.28%> (-0.01%)	⬇️
examples+coraza.rule.case_sensitive_args_keys	81.73% <100.00%> (+0.01%)	⬆️
examples+coraza.rule.multiphase_valuation	81.60% <100.00%> (+0.01%)	⬆️
examples+coraza.rule.no_regex_multiline	81.63% <100.00%> (+0.01%)	⬆️
examples+memoize_builders	81.73% <100.00%> (+0.01%)	⬆️
examples+no_fs_access	81.05% <100.00%> (+0.01%)	⬆️
ftw	81.77% <100.00%> (+0.01%)	⬆️
memoize_builders	81.86% <100.00%> (+0.01%)	⬆️
no_fs_access	81.22% <100.00%> (+0.01%)	⬆️
tinygo	81.74% <100.00%> (+0.01%)	⬆️

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