FXCM-2281: Integrate EncryptorDecryptor into the autofill database

[theidkamp]

What

The autofill store now owns its encryption context: Store::new() takes an EncryptorDecryptor (from the shared db-crypto crate, #7542) and passes it to the database. All code accessing the encrypted column obtains the
encryptor/decryptor from the database, so encryption keys no longer need to be passed through the sync API.

• constructor(string dbpath, EncryptorDecryptor encdec)
• scrub_undecryptable_credit_card_data_for_remote_replacement() no longer takes an encryption key.

This follows the same structure as logins on the db-crypto branch:

• autofill/src/encryption.rs has been removed. Call sites now use db_crypto types directly, string conversion lives next to its consumers, and the key-based UDL functions have moved to lib.rs.
• Factory functions matching the logins API were added as a workaround for the UniFFI/JS trait bug: create_static_key_manager, create_managed_encdec, create_autofill_store_with_static_key_manager,
  and behind the new keydb feature create_autofill_store_with_nss_keymanager (using the key name
  as-autofill-key).

Breaking changes

Code that constructs the store (or calls scrub) is affected, one call site per platform:

• Desktop: RustAutofillStore.sys.mjs (Store.init)
• Android: AutofillCreditCardsAddressesStorage.kt (store init, uses
  createAutofillStoreWithStaticKeyManager(dbPath, key) with the existing autofill key)
• iOS: RustAutofill.swift (store init + the scrub call, iOS is its only caller)

The sync engine also no longer implements set_local_encryption_key. The store owns
the encryptor, so there is nothing to hand over. Consumers must stop passing an
encryption key for creditcards in the sync manager's local_encryption_keys
before updating; passing one now hits sync15's default and panics at sync time
(a runtime break, not a compile break):

• Android: WorkManagerSyncManager.kt:410–414: drop the CreditCards keyProvider
  guard and its engineKeyProviders registration, leaving only
  registerWithSyncManager() (matching the Passwords branch)
• iOS: RustSyncManager.swift: drop localEncryptionKeys["creditcards"] = key

Blocked on #7542 this branch does not build until the shared crate lands.

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
• Quality: This PR builds and tests run cleanly
  • Note:
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• Tests: This PR includes thorough tests or an explanation of why it does not
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  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.