Allow read-only CALL procedures on the read path (access_mode=read)

[liulx20]

NeuG currently classifies standalone CALL as a non-read operation for access-mode gating. As a result, read-only procedures (e.g. GDS algorithms, SHOW_LOADED_EXTENSIONS) cannot run with explicit access_mode=read, even though they do not mutate the graph.

We should honor Function::isReadOnly when classifying TABLE_FUNCTION_CALL execution flags so read-only CALLs can use the read path, while mutating procedures remain rejected.

[github-actions]

🤖 Auto-triage: could not confidently classify this issue under any current v0.2 umbrella.

Reason: The issue is a small, targeted compiler/binder fix to honor Function::isReadOnly for CALL procedure access-mode gating, which does not fit any specific umbrella's scope and is too narrow for #49 or #257.

Auto-applied: type → Task; labels → compiler, executor

Maintainers: please pick a parent manually, or close if out of scope.