Add support for installing CI-built sdist/wheel (prefer uv when artifact present)

[anguzo]

Please allow Oryx Python builds to install from a user-provided distribution artifact (wheel or sdist) produced in CI, and prefer uv for installation when such an artifact is present. This preserves App Service’s non-container workflow while enabling modern pyproject-based pipelines and much faster, greener installs.

Since support for uv is coming (#2614, #2652) this should be easily achievable.

Why this is needed

• Oryx today expects requirements.txt and does dependency resolution/build on the platform. Many teams now build wheels/sdists in CI via pyproject backends (Poetry/uv/PEP 517) for reproducibility and speed.
• Installing a single artifact is deterministic, reduces network churn, and decouples resolution from the platform build.
• uv brings substantial install-time savings for packages; e.g., msgraph-sdk local machine example: pip ~8 minutes vs uv ~20 seconds. At App Service scale, defaulting to uv for artifact installs would materially lower build time, CPU usage, and energy consumption.

What to add

• Detection: If a single local distribution artifact exists (e.g., ./dist/*.whl or *.tar.gz)t, install it into the Oryx-managed venv.
• Precedence:
  • If exactly one artifact is found under ./dist or project root, install it.
• Installer preference:
  • Use uv to install the artifact by default (e.g., uv pip install ./my_app-1.0.0-py3-none-any.whl).
• Optional flags to consider:
  • Allow pass-through of safe install flags via env vars (e.g., PYTHON_UV_INSTALL_ARGS), and to enable following best practices (e.g., use --compile-bytecode).

Example workflow

• CI: uv build -> produces dist/app-1.0.0.whl (and/or sdist) -> include in the ZIP deployed to App Service.
• Oryx: detects artifact; installs via uv by default; standard startup command (e.g., gunicorn ... my_app:app).

Benefits

• Faster, greener builds: uv’s installer drastically reduces install time and CPU, improving latency and environmental impact.
• Modern packaging compatibility: supports pyproject workflows without containerizing.
• Reproducibility: dependency resolution and wheel building happen once in CI; Oryx installations are minimal and predictable.
• Backwards compatible: if no artifact is present, behavior remains unchanged.

Scope and safety

• Feature is opt-in via presence of an artifact.
• Clear precedence rules avoid surprises; fall back to requirements.txt if ambiguity exists.