fix: update 6 test files broken by dead code removal

- test_percentage_clamp.py: remove TestContextCompressorUsagePercent class
  and test_context_compressor_clamped (tested removed get_status() method)
- test_credential_pool.py: remove test_mark_used_increments_request_count
  (tested removed mark_used()), replace active_lease_count() calls with
  direct _active_leases dict access, remove mark_used from thread test
- test_session.py: replace SessionSource.local_cli() factory calls with
  direct SessionSource construction (local_cli classmethod removed)
- test_error_classifier.py: remove test_is_transient_property (tested
  removed is_transient property on ClassifiedError)
- test_delivery.py: remove TestDeliveryRouter class (tested removed
  resolve_targets method), clean up unused imports
- test_skills_hub.py: remove test_is_hub_installed (tested removed
  is_hub_installed method on HubLockFile)

tests/tools/test_skills_hub.py

@@ -854,16 +854,6 @@ class TestHubLockFile:
         names = {e["name"] for e in installed}
         assert names == {"s1", "s2"}
 
-    def test_is_hub_installed(self, tmp_path):
-        lock = HubLockFile(path=tmp_path / "lock.json")
-        lock.record_install(
-            name="my-skill", source="github", identifier="x",
-            trust_level="trusted", scan_verdict="pass",
-            skill_hash="h", install_path="my-skill", files=["SKILL.md"],
-        )
-        assert lock.is_hub_installed("my-skill") is True
-        assert lock.is_hub_installed("other") is False
-
 
 # ---------------------------------------------------------------------------
 # TapsManager