switch to anthropic-sdk-go for better stream control

[cpunion]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 59.42857% with 71 lines in your changes missing coverage. Please review.

Project coverage is 61.98%. Comparing base (d09c2a6) to head (5fa8733).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
examples/stream/main.go	0.00%	34 Missing ⚠️
providers/anthropic/anthropic_client.go	74.72%	19 Missing and 4 partials ⚠️
providers/openai/openai_client.go	73.46%	13 Missing ⚠️
examples/chat/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #2       +/-   ##
===========================================
- Coverage   74.18%   61.98%   -12.20%     
===========================================
  Files           7        8        +1     
  Lines         244      342       +98     
===========================================
+ Hits          181      212       +31     
- Misses         52      117       +65     
- Partials       11       13        +2     

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