Convert detectors to factory pattern, ability to set different model for each detector (#4635)

* refactor detectors

* move create_detector and DetectorTypeEnum

* fixed code formatting

* add detector model config models

* fix detector unit tests

* adjust SharedMemory size to largest detector model shape

* fix detector model config defaults

* enable auto-discovery of detectors

* simplify config

* simplify config changes further

* update detectors docs; detect detector configs dynamic

* add suggested changes

* remove custom detector doc

* fix grammar, adjust device defaults

frigate/detectors/plugins/cpu_tfl.py

@@ -0,0 +1,60 @@
+import logging
+import numpy as np
+
+from frigate.detectors.detection_api import DetectionApi
+from frigate.detectors.detector_config import BaseDetectorConfig
+from typing import Literal
+from pydantic import Extra, Field
+import tflite_runtime.interpreter as tflite
+
+
+logger = logging.getLogger(__name__)
+
+DETECTOR_KEY = "cpu"
+
+
+class CpuDetectorConfig(BaseDetectorConfig):
+    type: Literal[DETECTOR_KEY]
+    num_threads: int = Field(default=3, title="Number of detection threads")
+
+
+class CpuTfl(DetectionApi):
+    type_key = DETECTOR_KEY
+
+    def __init__(self, detector_config: CpuDetectorConfig):
+        self.interpreter = tflite.Interpreter(
+            model_path=detector_config.model.path or "/cpu_model.tflite",
+            num_threads=detector_config.num_threads or 3,
+        )
+
+        self.interpreter.allocate_tensors()
+
+        self.tensor_input_details = self.interpreter.get_input_details()
+        self.tensor_output_details = self.interpreter.get_output_details()
+
+    def detect_raw(self, tensor_input):
+        self.interpreter.set_tensor(self.tensor_input_details[0]["index"], tensor_input)
+        self.interpreter.invoke()
+
+        boxes = self.interpreter.tensor(self.tensor_output_details[0]["index"])()[0]
+        class_ids = self.interpreter.tensor(self.tensor_output_details[1]["index"])()[0]
+        scores = self.interpreter.tensor(self.tensor_output_details[2]["index"])()[0]
+        count = int(
+            self.interpreter.tensor(self.tensor_output_details[3]["index"])()[0]
+        )
+
+        detections = np.zeros((20, 6), np.float32)
+
+        for i in range(count):
+            if scores[i] < 0.4 or i == 20:
+                break
+            detections[i] = [
+                class_ids[i],
+                float(scores[i]),
+                boxes[i][0],
+                boxes[i][1],
+                boxes[i][2],
+                boxes[i][3],
+            ]
+
+        return detections