Fix installing from sdist (setup.py imports the package, pulling typing_extensions at build time)

[sethc555]

Installing resend from source currently fails in any isolated build:

$ docker run --rm python:3.12 pip install --no-binary :all: resend
...
ModuleNotFoundError: No module named 'typing_extensions'

setup.py imports the package to get __version__, which pulls typing_extensions into the build environment, and reads a requirements file not shipped in the sdist. This change reads the version statically (stdlib re over resend/version.py) and guards the file read with the pinned fallback.

Verified: with this change, python -m build (sdist → wheel built from that sdist) succeeds in a clean python:3.12 container; without it, it fails. Found while build-checking popular PyPI packages for source-install breakage (wheelproof).

Also verified: a wheel built from the patched 2.30.1 sdist is payload-identical to the published 2.30.1 wheel.

---

Summary by cubic

Fix sdist installs for resend by avoiding build-time package import and guarding a missing requirements.txt. Isolated source builds now succeed without needing typing_extensions preinstalled.

• Bug Fixes
  • Parse version from resend/version.py using stdlib re instead of importing the package.
  • Read requirements.txt only if present; otherwise use ["requests>=2.31.0", "typing_extensions>=4.4.0"].
  • Verified python -m build sdist→wheel works in a clean Python 3.12 container; wheel from patched 2.30.1 sdist matches the published wheel payload.

^{Written for commit 6a5ef9d. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Auto-approved: This is a low-risk build fix that replaces a package import with static version parsing and guards against a missing requirements file, with no impact on runtime logic or data integrity.

Re-trigger cubic</sub>