feat: Add GitHub Actions workflow for building and testing the Depth Anything 3 extension

- Create a build workflow in `.github/workflows/build.yml` to automate the build process.
- Configure Python environment and install dependencies.
- Add steps for running tests and packaging the extension.

chore: Initialize project metadata and dependencies for Depth Anything 3

- Add `pyproject.toml` for project configuration and dependencies.
- Include optional dependencies for app and gs functionalities.
- Define project scripts and metadata.

chore: Add requirements file for Depth Anything 3 dependencies

- Create `requirements.txt` listing all necessary packages for the project.

feat: Implement export utility functions for Depth Anything 3

- Create `src/depth_anything_3/utils/export/__init__.py` to handle various export formats.
- Implement functions for exporting predictions in different formats.

feat: Add ray utility functions for homography estimation

- Create `src/depth_anything_3/utils/ray_utils.py` with functions for computing optimal rotation and homography using RANSAC.

feat: Implement vendor preparation script

- Add `prepare_vendor.py` to manage third-party dependencies and artifacts.
- Include functions for downloading and verifying artifacts based on a lock file.

test: Add unit tests for vendor preparation script

- Create `tests/test_prepare_vendor.py` to test artifact downloading and verification.
- Implement tests for handling hash mismatches and unsupported platforms.

chore: Add vendor lock file for dependency management

- Create `vendor.lock.toml` to define artifacts and platforms for the project.

tests/test_prepare_vendor.py

@@ -0,0 +1,67 @@
+import hashlib
+import importlib.util
+import io
+import tempfile
+import unittest
+from pathlib import Path
+from unittest.mock import patch
+
+
+PROJECT_ROOT = Path(__file__).resolve().parents[1]
+
+
+def load_prepare_vendor():
+    specification = importlib.util.spec_from_file_location(
+        "snapform_prepare_vendor",
+        PROJECT_ROOT / "prepare_vendor.py",
+    )
+    module = importlib.util.module_from_spec(specification)
+    specification.loader.exec_module(module)
+    return module
+
+
+class PrepareVendorTest(unittest.TestCase):
+    def test_downloads_and_verifies_artifact(self):
+        prepare = load_prepare_vendor()
+        content = b"locked artifact"
+        artifact = {
+            "filename": "artifact.tar.gz",
+            "url": "https://example.invalid/artifact.tar.gz",
+            "sha256": hashlib.sha256(content).hexdigest(),
+        }
+        with tempfile.TemporaryDirectory() as directory, patch.object(
+            prepare.urllib.request,
+            "urlopen",
+            return_value=io.BytesIO(content),
+        ):
+            path = prepare.download_artifact(artifact, Path(directory))
+            self.assertEqual(path.read_bytes(), content)
+
+    def test_rejects_hash_mismatch_without_leaving_partial_file(self):
+        prepare = load_prepare_vendor()
+        artifact = {
+            "filename": "artifact.tar.gz",
+            "url": "https://example.invalid/artifact.tar.gz",
+            "sha256": hashlib.sha256(b"expected").hexdigest(),
+        }
+        with tempfile.TemporaryDirectory() as directory, patch.object(
+            prepare.urllib.request,
+            "urlopen",
+            return_value=io.BytesIO(b"unexpected"),
+        ):
+            destination = Path(directory)
+            with self.assertRaisesRegex(RuntimeError, "SHA-256 mismatch"):
+                prepare.download_artifact(artifact, destination)
+            self.assertFalse((destination / artifact["filename"]).exists())
+            self.assertFalse(
+                (destination / f"{artifact['filename']}.part").exists()
+            )
+
+    def test_rejects_unknown_platform(self):
+        prepare = load_prepare_vendor()
+        with self.assertRaisesRegex(ValueError, "Unsupported platform"):
+            prepare.prepare(["windows-arm64"])
+
+
+if __name__ == "__main__":
+    unittest.main()