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/compute/dynamips/test_dynamips_kernel_datapath.py

@@ -25,27 +25,24 @@ hypervisor's fds released before the TAPs are unpersisted — QEMU's order,
 since here it is Dynamips that holds them).
 """
 
+import contextlib
 import os
 import shutil
-import contextlib
+from unittest.mock import MagicMock, patch
 
 import pytest
 import pytest_asyncio
 
-from unittest.mock import MagicMock, patch
-
-from tests.utils import AsyncioMagicMock
-
 from gns3server.compute.dynamips import Dynamips
-from gns3server.compute.dynamips.nodes.router import Router
-from gns3server.compute.dynamips.dynamips_error import DynamipsError
 from gns3server.compute.dynamips.adapters.gt96100_fe import GT96100_FE
 from gns3server.compute.dynamips.adapters.pa_4t import PA_4T
 from gns3server.compute.dynamips.adapters.pa_fe_tx import PA_FE_TX
 from gns3server.compute.dynamips.adapters.wic_1enet import WIC_1ENET
-from gns3server.compute.ubridge.ubridge_error import UbridgeError
+from gns3server.compute.dynamips.dynamips_error import DynamipsError
+from gns3server.compute.dynamips.nodes.router import Router
 from gns3server.compute.nios.nio_bridge import NIOBridge
-
+from gns3server.compute.ubridge.ubridge_error import UbridgeError
+from tests.utils import AsyncioMagicMock
 
 NODE_ID = "00010203-0405-0607-0809-0a0b0c0d0e0f"
 BRIDGE = "gns3a1b2c3d4e5f"
@@ -237,7 +234,7 @@ async def test_prepare_tap_datapath_wires_nios_bound_while_stopped(router):
 
     hypervisor = _hypervisor_commands(router)
     assert any(c.startswith("nio create_tap tap-") and c.endswith(f"{TAP00}") for c in hypervisor)
-    assert any(c.startswith(f"vm slot_add_nio_binding \"R1\" 0 0 tap-") for c in hypervisor)
+    assert any(c.startswith('vm slot_add_nio_binding "R1" 0 0 tap-') for c in hypervisor)
     router._ubridge_send.assert_any_call(f'brctl addif "{BRIDGE}" "{TAP00}"')
     assert (0, 0) in router._tap_nios
 
@@ -489,9 +486,7 @@ async def test_stop_ubridge_releases_hypervisor_fds_before_deleting_taps(router)
     router._ubridge_send.reset_mock()
     router._hypervisor.commands.clear()
 
-    with patch(
-        "gns3server.compute.base_node.BaseNode._stop_ubridge", new=AsyncioMagicMock()
-    ) as stop:
+    with patch("gns3server.compute.base_node.BaseNode._stop_ubridge", new=AsyncioMagicMock()) as stop:
         await router._stop_ubridge()
 
     hypervisor = _hypervisor_commands(router)