Add new exceptions types and improve tests

[mstuttgart]

Proposed change

Add new exceptions to encapsulate requests exceptions and improve BrazilCEP API and docs

Type of change

• New CEP API support (thank you!)
• Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• Dependency update (version deprecation/pin/upgrade)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (a code change causing existing functionality to break)
• New feature (new brazilcep functionality in general)

Checklist

• I've followed the contributing guidelines
• I've successfully run make check, all checks and tests are green

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (28bdc20) to head (2c97760).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #99   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines           76       116   +40     
  Branches        12        13    +1     
=========================================
+ Hits            76       116   +40     

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