chore(lint): make the repository ruff-clean under the strict select

Clear the deferred full-repo lint backlog so the whole tree passes the strict
ruff select (E,W,F,I,B,UP,C4,SIM). Mechanical fixes dominate: import sorting,
pep585/604 annotations, dropped dead imports, and whitespace. The few semantic
changes are behavior-preserving: declare __all__ on the agent_utils and
alpha_vantage re-export hubs; expand 'from x import *' to explicit names; use
immutable tuple defaults instead of mutable list defaults; contextlib.suppress
for try/except/pass; and narrow an over-broad assertRaises.

tests/test_openai_compatible_provider.py

@@ -4,7 +4,6 @@ Verifies the user-supplied base_url is required and honored, the key is optional
 (keyless local default), Chat Completions (not the Responses API) is used, any
 model name is accepted, and the env backend URL precedence (#978).
 """
-import os
 
 import pytest