build: route Python restores through CFS

[Fabio Cavalcante (fabiocav)]

Summary

• Route every repository-owned Azure Pipelines Python install job through azfunc/public/upstream-public.
• Run PipAuthenticate@1 before UsePythonVersion@0 and explicitly replace the primary index with onlyAddExtraIndex: false.
• Remove the legacy per-pipeline feed parameter and old PythonExtensions_*PublicPackages feed references.
• Leave customer samples, requirements files, release upload destinations, and dependency manifests unchanged; no pip configuration is committed.

EM owner: @vameru

Validation

• Parsed all 13 YAML files and structurally verified all 10 Python-installing jobs have exactly one correctly configured authentication task before Python setup and package installation.
• Resolved all seven package development/runtime graphs from empty caches through CFS in a checkout path containing spaces, using structured command arguments.
• Recorded 716 CFS resolver-host matches and zero direct requests to pypi.org, files.pythonhosted.org, npmjs, or nuget.org across 32 resolver logs.
• Passed 314 tests across base, Blob, Cosmos DB, Event Hubs, Service Bus, FastAPI, and Connectors. Three Blob downloader tests requiring live Azure Storage were deselected locally.
• Downloaded complete binary graphs from empty caches for CPython 3.9 and 3.13 on Windows, Linux, and macOS (62/73 files per platform), plus the CPython 3.11 Windows build/audit tool graph (44 files).
• Built and checked seven wheels plus seven source distributions; smoke-installed and imported all seven wheels; all seven pip-audit runs reported no known vulnerabilities.
• Audited archives and the worktree: no feed configuration, credentials, lockfiles, node_modules, committed pip config, or manifest rewrites were introduced.

Surface audit

The repository owns Python packaging and Azure Pipelines install surfaces. It has no repository-owned npm project, NuGet/.NET project, uv usage, or Dockerfile requiring CFS changes. GitHub Actions contains only a PR-title check and performs no package installation.