Add packaging functions to Tower SDK

[bradhe]

This PR is our first bit of functionality exposing rust code to the Python SDK. It adds a new function build_package that creates a package that can be used for deployments to Tower.

Summary by CodeRabbit

Release Notes

• New Features

  • Tower is now available as a native Python package with a build_package() function for programmatic use.
  • Tower CLI is now directly callable from Python.

• Tests

  • Added comprehensive test coverage for package building functionality.

• Chores

  • Improved build system to support multiple Python versions.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch tasks/add-packaging-to-tower-sdk

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[konstantinoscs]

What changed and we need this?

[bradhe]

We had many interpreters available in the OS, we had to tell it specifically which one to use. It's complicated.

[konstantinoscs]

I..... trust you

[konstantinoscs]

nit: rt was not very descriptive here and I had to look for the declaration.

[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In @.github/workflows/build-binaries.yml:
- Line 109: Add the pip flag --no-index to every CI install invocation that
currently uses --find-links so pip won’t fallback to PyPI; update the
occurrences of "pip install ${{ env.PACKAGE_NAME }} --find-links dist/
--force-reinstall", the "python -m pip install" call, the standalone "pip
install" and "pip3 install" invocations, and the ".venv/bin/pip3 install"
commands to include --no-index (place it alongside --find-links/other flags) so
the tests only use the local dist artifacts.
- Around line 126-129: The workflow uses an invalid Maturin interpreter flag
value "interpreter: -i 3.13"; change that entry to provide an executable name
(e.g., "interpreter: -i python3" or "interpreter: -i python3.13") so the ARM
aarch64 build uses a valid --interpreter value; update the "interpreter: -i
3.13" line to match the other builds' "interpreter: -i python3" (or a specific
python executable) to avoid Maturin failing.

🧹 Nitpick comments (2)

src/tower/__init__.py (1)

28-29: Consider deferring native import failure for better UX.

A guarded import would keep the package importable and surface a clearer error only when build_package is actually called.

♻️ Suggested change

-from ._native import build_package
+try:
+    from ._native import build_package
+except Exception as exc:
+    def build_package(*args, **kwargs):
+        raise RuntimeError(
+            "tower._native extension is not available. Reinstall with a compatible wheel "
+            "or build from source with Rust."
+        ) from exc

tests/tower/test_build_package.py (1)

28-36: Close extracted file handles in _read_package.

tar.extractfile() returns a file-like object (io.BufferedReader) that should be closed to prevent file descriptor leaks when reading many entries.

♻️ Suggested change

-            if member.isfile():
-                f = tar.extractfile(member)
-                entries[member.name] = f.read().decode("utf-8") if f else ""
+            if member.isfile():
+                f = tar.extractfile(member)
+                if f:
+                    with f:
+                        entries[member.name] = f.read().decode("utf-8")
+                else:
+                    entries[member.name] = ""