[BUG] Fix schema name sanitization for OpenAI API compatibility

[alexey-hunter-io]

What this does

Sanitizes schema names in build_schema_payload by replacing characters that don't match [a-zA-Z0-9_-] with _.

Since v1.13.0, normalize_schema_payload preserves the :name key from to_json_schema. When using ruby_llm-schema, the schema name defaults to the full Ruby class name (e.g. MyApp::Nested::Schema) which contains ::. OpenAI requires response_format.json_schema.name to match ^[a-zA-Z0-9_-]+$, so the request is rejected with a BadRequestError.

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

Fixes #654