perf(track): avoid per-frame allocations and list lookups in tracker (#23523)

Two small per-object-per-frame improvements in the tracker hot path
(match_and_update), both bit-identical:

- get_stationary_threshold returned a freshly constructed StationaryThresholds
  (a dataclass plus a list) on every call for any label not in the three
  known lists - i.e. for common labels like person/dog. The default thresholds
  are constant and never mutated, so return a shared module-level singleton,
  as the other three cases already do.
- untracked_object_boxes membership used `box not in [list of boxes]` (O(n));
  build a set of box tuples for O(1) membership. Boxes are hashable as tuples
  and output is unchanged.

get_stationary_threshold appeared in a live py-spy --gil profile of a camera
process_frames worker. Adds tests for the threshold lookups.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frigate/test/test_stationary_classifier.py

@@ -0,0 +1,39 @@
+"""Tests for stationary object classification thresholds."""
+
+import unittest
+
+from frigate.track.stationary_classifier import (
+    DEFAULT_OBJECT_THRESHOLDS,
+    DYNAMIC_OBJECT_THRESHOLDS,
+    NON_STATIONARY_OBJECT_THRESHOLDS,
+    STATIONARY_OBJECT_THRESHOLDS,
+    StationaryThresholds,
+    get_stationary_threshold,
+)
+
+
+class TestStationaryThresholds(unittest.TestCase):
+    def test_known_labels_return_expected_singletons(self) -> None:
+        self.assertIs(get_stationary_threshold("package"), STATIONARY_OBJECT_THRESHOLDS)
+        self.assertIs(get_stationary_threshold("car"), DYNAMIC_OBJECT_THRESHOLDS)
+        self.assertIs(
+            get_stationary_threshold("license_plate"),
+            NON_STATIONARY_OBJECT_THRESHOLDS,
+        )
+
+    def test_unknown_label_returns_shared_default(self) -> None:
+        # an unknown label must reuse the shared default instance, not allocate
+        # a fresh one on every call (this runs per object per frame)
+        first = get_stationary_threshold("person")
+        second = get_stationary_threshold("dog")
+        self.assertIs(first, DEFAULT_OBJECT_THRESHOLDS)
+        self.assertIs(second, DEFAULT_OBJECT_THRESHOLDS)
+
+    def test_default_matches_a_fresh_instance(self) -> None:
+        # the shared default must be value-equivalent to the previous
+        # per-call StationaryThresholds()
+        self.assertEqual(DEFAULT_OBJECT_THRESHOLDS, StationaryThresholds())
+
+
+if __name__ == "__main__":
+    unittest.main()