Enable Streaming for OpenAI-compatible models

[svilupp]

Updated

• Enabled Streaming for OpenAI-compatible APIs (eg, DeepSeek Coder)
• If streaming to stdout, also print a newline at the end of streaming (to separate multiple outputs).

Fixed

• Relaxed the type-assertions in StreamCallback to allow for more flexibility.

[codecov]

Codecov Report

Attention: Patch coverage is 12.00000% with 22 lines in your changes missing coverage. Please review.

Project coverage is 91.39%. Comparing base (f20f3b9) to head (e1c8fdf).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/llm_openai.jl	8.69%	21 Missing ⚠️
src/streaming.jl	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
- Coverage   91.76%   91.39%   -0.38%     
==========================================
  Files          46       46              
  Lines        4360     4415      +55     
==========================================
+ Hits         4001     4035      +34     
- Misses        359      380      +21     

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