DIDComm Message Format Inconsistency

[b901]

What

As a developer using the didcomm-swift library in a mobile app, I want the library to consistently use snake_case for created_time and expires_time fields in DIDComm messages, so that it follows the DIDComm specification and ensures consistency across all platforms.

Why

• The current implementation in the didcomm-swift library might be inconsistent in its use of snake_case (created_time and expires_time) for these fields, which should match the DIDComm specification.
• This inconsistency causes the message that is packed on the iOS side to not have fields created_time and expires_time when unpacked on the Android side. Packing on the Android side follows the didcomm spec and these fields use snake case correctly.

Success Criteria

• [ ] Ensure that messages that are packed on the iOS side have the created_time and expires_time fields when unpacked on the Android side.

Anything else

• Link to relevant code: https://github.com/sicpa-dlab/didcomm-rust/blob/4388350def84b6d7f6b65cf4a451607200035d8d/wrappers/swift/didcomm/didcomm.swift#L1378
• Link to didcomm spec: https://identity.foundation/didcomm-messaging/spec/v2.1/#plaintext-message-structure