Add support for RubyLLM 2.0

[David Elner (delner)]

Adds support for ruby_llm 2.0, released 2026-09-18. Our integration covered 1.x only, and 2.0 is a breaking major release that moves most of what the instrumentation reads.

What 2.0 changed

Area	1.x	2.0	Support added
Message attachments	message.content.attachments on a RubyLLM::Content	message.attachments; Content removed, content is a String	Read either shape, so attachments reach traces again
Tool schema	tool.params_schema, Providers::OpenAI::Tools	tool.parameters_schema; provider Tools module removed	Read either, so tool spans carry real parameters instead of {}
OpenAI endpoint	Chat Completions	Responses API by default	Recorded Responses cassettes; each version replays its own endpoint
Tool DSL	param ..., desc:	parameter ..., description:	Tests use whichever the loaded version exposes
Chat#with_tool	present	removed, with_tools remains	Tests use with_tools, valid on both

Version differences are handled by duck-typing what the object exposes rather than branching on a version number, so 1.x and 2.0 run the same code path.

[Abhijeet Prasad (AbhiPrasad)]

do we want to version cassettes by library version? And then have a test matrix of versions we test against?

[Stephen Belanger (Qard)]

Generally LGTM, but I agree it might be a good idea to version things explicitly. The different endpoints is an implementation detail which could change, that doesn't explicitly reflect the version.

[David Elner (delner)]

Good suggestion: put them under major versions.