chore: Correct type annotations and add mypy for code checking

[chyroc]

• Fixed type annotation issues across the codebase
• Added mypy as a development dependency
• Implemented mypy for static type checking to ensure type safety and correctness

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.76%. Comparing base (24a371b) to head (685d143).
Report is 3 commits behind head on main.

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
+ Coverage   98.74%   98.76%   +0.02%     
==========================================
  Files          38       38              
  Lines        2303     2343      +40     
==========================================
+ Hits         2274     2314      +40     
  Misses         29       29              

Files with missing lines	Coverage Δ
cozepy/auth/__init__.py	93.10% <100.00%> (+0.14%)	⬆️
cozepy/bots/__init__.py	100.00% <100.00%> (ø)
cozepy/chat/__init__.py	100.00% <100.00%> (ø)
cozepy/chat/message/__init__.py	100.00% <100.00%> (ø)
cozepy/conversations/__init__.py	100.00% <100.00%> (ø)
cozepy/conversations/message/__init__.py	100.00% <100.00%> (ø)
cozepy/coze.py	100.00% <100.00%> (ø)
cozepy/exception.py	100.00% <100.00%> (ø)
cozepy/files/__init__.py	100.00% <100.00%> (ø)
cozepy/knowledge/__init__.py	100.00% <100.00%> (ø)
... and 15 more