fix: repos with very large entries (e.g. Brave) fail to sync with "Error parsing index"

[Victor-root]

🐛 What's broken

Adding a repository that contains a single very large entry — like the
Brave Browser repos, which bundle hundreds of releases for one package —
fails to sync. The repo shows as added, but you get an Error parsing index
notification and never receive its apps.

Root cause: that entry serializes to a > 2 MB blob, and SQLite's per-row
CursorWindow is capped at ~2 MB. Reading the row throws
SQLiteBlobTooBigException — both while merging the downloaded index
(IndexMerger) and when reading the full product from the database
(ProductAdapter).

🔧 The fix

Gzip-compress the large serialized blobs before storing them, and decompress
on read. JSON shrinks ~5–10×, which keeps these rows comfortably under the limit.
This can affect any repo with an oversized entry, not just Brave, so the fix
is global.

• 📦 New ByteArray.gzip() / gunzipIfNeeded() helpers
• 🗃️ Compress product & release blobs in IndexMerger (sync/merge path)
• 🗄️ Compress ROW_DATA in ProductAdapter (app-detail path)

♻️ Backward compatible

Reads auto-detect the gzip header, so rows written before this change still
parse — no DB migration and no forced re-sync.

🧪 Testing

• ✅ Unit tests for the compress/decompress round-trip + legacy passthrough
• ✅ Built and tested on a physical device (Oppo Reno 13 Pro, Android 16):
  both Brave Beta repos now sync cleanly