fix(npm): retry transient installer downloads

[hpouillot]

Summary

• retry transient npm installer downloads with four total attempts and 1s/2s/4s exponential backoff
• retry the complete response stream, including mid-transfer disconnects, while failing permanent errors such as HTTP 404 immediately
• add focused Node tests, CI coverage, and updated installer snapshots
• prepare the 0.32.1 patch release with workspace version and changelog updates

This makes the workaround in PostHog/posthog#82416 unnecessary once consumers upgrade to cargo-dist 0.32.1, and extends the retry work from #2311 to the generated npm installer.

Testing

• node --test cargo-dist/tests/npm-installer.test.js
• npx prettier --check cargo-dist/templates/installer/npm/*.js cargo-dist/tests/npm-installer.test.js
• cargo fmt --all -- --check
• cargo test --workspace -- --test-threads=1