feat: Add Device Auth flow with error handling

[chyroc]

• Implemented device auth flow including obtaining device code, token exchange, and token refresh
• Added support for handling PKCE flow errors like authorization_pending, slow_down, access_denied and expired_token

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 34.54545% with 36 lines in your changes missing coverage. Please review.

Project coverage is 72.47%. Comparing base (cf1d373) to head (31a050e). Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
cozepy/auth/__init__.py	20.51%	31 Missing :warning:
cozepy/request.py	66.66%	3 Missing :warning:
cozepy/exception.py	60.00%	2 Missing :warning:

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
- Coverage   74.59%   72.47%   -2.12%     
==========================================
  Files          30       30              
  Lines        1055     1101      +46     
==========================================
+ Hits          787      798      +11     
- Misses        268      303      +35     

Flag	Coverage Δ
	72.47% <34.54%> (-2.12%)	:arrow_down:

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Files with missing lines	Coverage Δ
cozepy/__init__.py	100.00% <100.00%> (ø)
cozepy/exception.py	68.18% <60.00%> (-2.41%)	:arrow_down:
cozepy/request.py	76.31% <66.66%> (-2.56%)	:arrow_down:
cozepy/auth/__init__.py	66.26% <20.51%> (-13.74%)	:arrow_down: