refactor: Merge Chat and Workflow Iterator into a generic Stream Iterator

[chyroc]

• Merged ChatChatIterator and WorkflowIterator into a single generic Stream Iterator
• Unified iterator to support both Chat and Workflow module

[codecov]

Codecov Report

Attention: Patch coverage is 67.14286% with 23 lines in your changes missing coverage. Please review.

Project coverage is 76.51%. Comparing base (23a6785) to head (632e688).
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
cozepy/workflows/runs/__init__.py	17.64%	14 Missing ⚠️
tests/test_workflow.py	20.00%	4 Missing ⚠️
cozepy/chat/__init__.py	81.25%	3 Missing ⚠️
cozepy/model.py	93.33%	2 Missing ⚠️

@@            Coverage Diff             @@
##             main      #32      +/-   ##
==========================================
+ Coverage   74.80%   76.51%   +1.70%     
==========================================
  Files          30       30              
  Lines        1028     1009      -19     
==========================================
+ Hits          769      772       +3     
+ Misses        259      237      -22     

Flag	Coverage Δ
	76.51% <67.14%> (+1.70%)	⬆️

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Files with missing lines	Coverage Δ
cozepy/__init__.py	100.00% <ø> (ø)
tests/test_chat.py	100.00% <100.00%> (ø)
cozepy/model.py	78.12% <93.33%> (+11.45%)	⬆️
cozepy/chat/__init__.py	84.73% <81.25%> (-0.24%)	⬇️
tests/test_workflow.py	25.00% <20.00%> (ø)
cozepy/workflows/runs/__init__.py	62.50% <17.64%> (+13.06%)	⬆️