[Fix] Properly raise rate limit errors from Anthropic

[orthodoX]

What this does

This fix should help to properly raise error messages like this one 👇🏻 as rate limit errors:

Anthropic rate limit messages mention "input tokens per minute/hour/day", which matches the /input[_\s-]?token/i pattern in the Error class, and those get misinterpreted as ContextLengthExceededError. These are genuine rate limits, so we should check for rate limit language first and raise RateLimitError instead.

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

Required for new features

• I opened an issue before writing code and received maintainer approval
• Linked issue: #___

PRs for new features or enhancements without a prior approved issue will be closed.

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.04%. Comparing base (4942d6c) to head (a8582e1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #722      +/-   ##
==========================================
- Coverage   87.05%   87.04%   -0.02%     
==========================================
  Files         119      119              
  Lines        5594     5596       +2     
  Branches     1407     1408       +1     
==========================================
+ Hits         4870     4871       +1     
- Misses        724      725       +1     

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