Fix method redefined warning for log_regexp_timeout= (Ruby 4.0+)

[dominion525]

What this does

On Ruby 4.0+, require "ruby_llm" emits:

warning: method redefined; discarding old log_regexp_timeout=

The option class method generates a setter via attr_accessor, which is then
overridden by the custom log_regexp_timeout= setter. This adds remove_method
before the redefinition to suppress the warning. A regression spec is included.

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
  • 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

• No API changes