feat: cache email RSA CryptoKeys by public key

[AmarBego]

Description

• Bug fix
• Feature enhancement
• Documentation update

The email decrypt path currently imports the matching per-vault RSA private key from its JWK string every time an email/data is decrypted, this happens in decryptEmail, decryptEmailList and decryptAttachment

What changed now is not the vault schema rather we introduced a cache that caches keys as non-exctractable CryptoKey objects for the unlocked client session. The cache is keyed by the existing public-key match EncyptionKey.PublicKey === email.encryptionKey so it supports multiple RSA keys for future key rotation instead of assuming a single vault key. The cache is cleared when in-memory vault/session is cleared or locked. In the extension i also manually verified that opening the Emails tab imports once and subsequent email opens reuse the cached key whilst logout clears the cache

Related Issues

• [Feature Request] Cache non-extractable CryptoKeys for client-side email decryption #2081

Checklist

• Code adheres to project standards and guidelines.
• Documentation has been updated where applicable.

[lanedirt]

Hi @AmarBego, just tested it locally and seems to work fine. Thanks for the work on this. LGTM!