fix: repair imports lost in the 3.1 rebase and meet the new lint baseline

The rebase onto upstream 3.1 (mypy + ruff I001/F401 waves) left the tree
short of the newly enforced baselines in three ways:

* contextlib / UbridgeError imports dropped as false duplicates during
  conflict resolution left NameErrors in iou_vm and qemu_vm (F821);
  the Dynamips router grabbed the compute-level NIOTAP instead of the
  hypervisor one, breaking TAP anchoring (test failure).
* unused imports (KERNEL_UNSUPPORTED_FILTERS, UbridgeError, List) and
  unsorted blocks left behind where the stack's later commits moved the
  last usage elsewhere — ruff I001/F401/RUF022 now enforce these.
* mypy, now baseline-free: cache dict annotations in tc_probe, the
  locators candidate list, the resolved-params None branch in the MCP
  runner, and validate_bpf_syntax keeps the upstream Dict[str, Any]
  return (the strict Optional[str] was wrong for the "valid" bool entry).

The e2e raw-frame probe resolves its compiler via shutil.which (S607)
and zips with strict= (B905); the remaining subprocess call is S603 by
nature and gets a per-file ignore like other test files.

ruff check/format clean, mypy at upstream parity (no new errors),
full unit suite 2167 passed.

tests/api/routes/compute/test_capabilities.py

@@ -170,7 +170,9 @@ class TestCapabilitiesRoutes:
         async def fake_bridge_tap_probe():
             return True
 
-        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", fake_bridge_tap_probe)
+        monkeypatch.setattr(
+            "gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", fake_bridge_tap_probe
+        )
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))