Add Metadata pattern and AsMetadata type class

[lsrcz]

Directly manipulating S-expressions can be hard. This pull request adds a type class AsMetadata to help it.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 75.24%. Comparing base (c9c04f5) to head (3337fa3).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Grisette/Internal/Core/Data/Symbol.hs	50.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
- Coverage   75.24%   75.24%   -0.01%     
==========================================
  Files         208      208              
  Lines       30938    30942       +4     
  Branches     2189     2187       -2     
==========================================
+ Hits        23280    23281       +1     
- Misses       5469     5474       +5     
+ Partials     2189     2187       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.