Upgraded `encodeAssetId` and `decodeAssetId` to use `aes-256-gcm` (Authenticated Encryption) instead of `aes-256-cbc`.
AES-CBC lacks authentication, leaving it potentially susceptible to padding oracle attacks or ciphertext manipulation.
The new token adds a `v2:` prefix which strictly enforces AES-GCM while supporting legacy fallback for cached urls.
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>