Fix Bedrock non-streaming thinking_tokens always returning nil

[alexmamrenko]

What this does

The Bedrock Converse API returns thinking/reasoning token counts nested under usage.outputTokensDetails.reasoningTokens, not at the top-level usage.reasoningTokens.

The streaming parser already handles this correctly via extract_reasoning_tokens in bedrock/streaming.rb:

def extract_reasoning_tokens(metadata_usage, usage)
  metadata_usage['reasoningTokens'] || usage['reasoningTokens'] ||
    usage.dig('output_tokens_details', 'thinking_tokens')
end

But parse_completion_response in bedrock/chat.rb only checked the top-level key:

thinking_tokens: usage['reasoningTokens'],

This caused thinking_tokens to always be nil for non-streaming Bedrock requests (e.g. chat.ask).

The fix adds the nested key fallback to match the streaming parser's behavior:

thinking_tokens: usage['reasoningTokens'] || usage.dig('outputTokensDetails', 'reasoningTokens'),

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • All tests pass: bundle exec rspec
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

AI-generated code

• I used AI tools to help write this code
• I have reviewed and understand all generated code (required if above is checked)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

[alexmamrenko]

Failed rubocop is not related to my changes