✨🐛 #183: Fix Anthropic API key header and start counting its token usage

[roma-glushko]

Anthropic seems to go out of beta finally and I could get a token to test our integration which doesn't seem to work because of the wrong API key header used.

Changes

• Fixed the header where Anthropic API key is passed
• Started propagating token usage of Anthropic requests
• Corrected the TokenUsage interface by changing count field to integers from floats

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 66.55%. Comparing base (369ddea) to head (5f763d7).

Files	Patch %	Lines
pkg/providers/anthropic/chat.go	77.27%	4 Missing and 1 partial ⚠️
pkg/providers/bedrock/chat.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #184      +/-   ##
===========================================
- Coverage    66.58%   66.55%   -0.04%     
===========================================
  Files           73       73              
  Lines         3163     3169       +6     
===========================================
+ Hits          2106     2109       +3     
- Misses         948      951       +3     
  Partials       109      109              

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[roma-glushko]

cc @curi-adi