fix(ci): the plugin API check compares a used function's signature, not only that it exists

[AlexS-scale]

Follow-up to #234. The plugin API check passes each USED entry's old and new object to griffe.find_breaking_changes. griffe compares only an object's members, so for a function it reports nothing. Every function listed in USED by itself was checked only for existence: for example, making count_runs's task_id required, or removing a parameter, passed without a !. That covers #234's run-index functions (insert_run, mark_terminal, …), find_task_instance, task_instances, build_env_provider and register_env_instance. Functions reached through a module entry (agent_env.plugins.settings) were already checked.

Now a function entry is compared through its parent module or class, and only its own breakages are kept.

The check still passes on main. Tests: a new used-function-signature-changed case fails before this change. An unused-sibling-of-a-used-function case shows that changing a function in the same module that isn't on the surface still passes.

Confidence Score: 5/5

The PR appears safe to merge; the requested sibling-filtering test is now present.

Summary

The PR makes the plugin API check catch signature changes to individually listed functions.

• The plugin API check now catches signature changes to used functions.

_{Reviews (2) · Last reviewed commit: "test(ci): a change to a used function's ..." · Reviewed by Greptile}