refactor: Refactor CozePKCEAuthError to use CozePKCEAuthErrorType Enum

[chyroc]

• Replaced Literal["authorizationpending", "slowdown", "accessdenied", "expiredtoken"] with CozePKCEAuthErrorType Enum
• Optimized type annotations for CozePKCEAuthError

[codecov]

Codecov Report

Attention: Patch coverage is 80.95238% with 4 lines in your changes missing coverage. Please review.

Project coverage is 98.74%. Comparing base (835e22c) to head (35c3a0a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cozepy/auth/__init__.py	20.00%	4 Missing ⚠️

@@           Coverage Diff           @@
##             main      #58   +/-   ##
=======================================
  Coverage   98.73%   98.74%           
=======================================
  Files          38       38           
  Lines        2298     2304    +6     
=======================================
+ Hits         2269     2275    +6     
  Misses         29       29           

Files with missing lines	Coverage Δ
cozepy/__init__.py	100.00% <100.00%> (ø)
cozepy/exception.py	100.00% <100.00%> (ø)
cozepy/request.py	97.93% <100.00%> (ø)
tests/test_auth.py	100.00% <ø> (ø)
tests/test_exception.py	100.00% <100.00%> (ø)
cozepy/auth/__init__.py	92.95% <20.00%> (ø)