Function initializeDriverWithAccountCredentials

Resolve + initialize a signature provider driver for an account, using the Credential Engine.

Mirrors MJStorage's initializeDriverWithAccountCredentials:

1. Resolve the driver by provider.ServerDriverKey via MJGlobal.ClassFactory.
2. Merge provider Configuration (defaults) + account Configuration (overrides) into the base config.
3. If the account has a CredentialID, decrypt it via the Credential Engine and overlay the values, wiring an onTokenRefresh callback that persists rotated tokens back via updateCredential.
4. Call driver.initialize(...).

Credential values take precedence over Configuration, matching the Storage merge order.