6.7.12

fix(llma): LangChain 1.0+ compatibility for CallbackHandler (#363)

* fix: Add LangChain 1.0+ compatibility for CallbackHandler imports

- Use try/except to import from langchain_core first (LangChain 1.0+)
- Fall back to legacy langchain imports for older versions
- Maintains backward compatibility with LangChain 0.x
- All existing tests pass (45 passed)

Fixes #362

* test: Add regression test for AgentAction/AgentFinish imports

- Tests that AgentAction and AgentFinish can be imported
- Tests on_agent_action and on_agent_finish callbacks with mock data
- Ensures compatibility with both LangChain 0.x and 1.0+
- Catches the import issue that was previously only tested with API keys

This addresses a test coverage gap identified during code review.

* chore: Add CHANGELOG entry for LangChain 1.0+ compatibility fix

* fix: Remove unused type: ignore comments for mypy

The type: ignore comments were only needed when the except block
executes, but CI runs with LangChain 1.0+ so the try block succeeds.
Mypy flags these as unused-ignore errors.

* chore: bump version to 6.7.12 for langchain 1.0 compatibility