Preserve PyPI versions without files

[AgentGoose32]

Refs #301

Preserves PyPI versions even when PyPI reports a release with no downloadable files.

The web package currently exposes release numbers in PyPI JSON, but each release has an empty file list. Previously that branch created a very sparse placeholder. This change keeps the version entry while enriching it from the per-version PyPI JSON endpoint.

Changes:

• Handles empty PyPI release file arrays via release_file = v.first
• Fetches per-version info metadata for no-file releases
• Preserves licenses, requires_python, yanked, and yanked_reason where available
• Marks those entries with metadata[:no_release_files] = true
• Keeps normal file-backed release behavior unchanged, just replacing v[0] with release_file

Validation:

• ruby -c app/models/ecosystem/pypi.rb
• git diff --check

Notes:

• Full Rails tests remain locally blocked by the repo lockfile requiring Bundler 4.0.10 under system Ruby.