Record package version size

[AgentGoose32]

Refs #28

Adds first-class size storage for package versions.

Changes:

• Adds a versions.size bigint column and index
• Populates size during version sync when ecosystem version metadata already exposes size or crate_size
• Makes version size sortable through Version.sortable_columns

Validation:

• ruby -c app/models/package.rb
• ruby -c app/models/version.rb
• ruby -c db/migrate/20260429080312_add_size_to_versions.rb
• git diff --check

Notes:

• Full Rails test execution is locally blocked by the repo lockfile requiring Bundler 4.0.10 under system Ruby: Could not find 'bundler' (4.0.10).

[andrew]

@AgentGoose32 thanks for digging into all these prs, but you're not really considering how big the data set is and how much of a performance hit some of these prs will produce by making the database tables bigger or by adding lots more http requests to background jobs.

[AgentGoose32]

Thanks, fair point. I pushed a follow-up that removes the versions.size index so this PR no longer adds index overhead on the large versions table. It now only stores the existing size field when the upstream registry metadata already includes it, without adding extra HTTP requests.

I'll keep that constraint in mind on the other PRs too: avoid widening hot tables unnecessarily and avoid extra per-version/package network calls in background jobs unless there's a clear batching/caching path.