Include entire sam3 package instead of just sam3 and sam3.model (#327)

Summary:
there are several imports within the `sam3.model` package that reference other packages within `sam3` other than `sam3` and `sam3.model` (for example [here](https://github.com/facebookresearch/sam3/blob/main/sam3/model/sam3_tracker_base.py#L15)).  This fixes the package structure so that you can `pip install` the package and `import sam3`

Pull Request resolved: https://github.com/facebookresearch/sam3/pull/327

Reviewed By: haithamkhedr

Differential Revision: D88950127

Pulled By: lematt1991

fbshipit-source-id: 3554512d304ccdf679a9af8606bbfe1f7f2a1cfb

sam3/model_builder.py

@@ -3,6 +3,8 @@
 import os
 from typing import Optional
 
+import pkg_resources
+
 import torch
 import torch.nn as nn
 from huggingface_hub import hf_hub_download
@@ -580,9 +582,10 @@ def build_sam3_image_model(
         A SAM3 image model
     """
     if bpe_path is None:
-        bpe_path = os.path.join(
-            os.path.dirname(__file__), "..", "assets", "bpe_simple_vocab_16e6.txt.gz"
+        bpe_path = pkg_resources.resource_filename(
+            "sam3", "assets/bpe_simple_vocab_16e6.txt.gz"
         )
+
     # Create visual components
     compile_mode = "default" if compile else None
     vision_encoder = _create_vision_backbone(
@@ -668,8 +671,8 @@ def build_sam3_video_model(
         Sam3VideoInferenceWithInstanceInteractivity: The instantiated dense tracking model
     """
     if bpe_path is None:
-        bpe_path = os.path.join(
-            os.path.dirname(__file__), "..", "assets", "bpe_simple_vocab_16e6.txt.gz"
+        bpe_path = pkg_resources.resource_filename(
+            "sam3", "assets/bpe_simple_vocab_16e6.txt.gz"
         )
 
     # Build Tracker module