[RC] Split Milliseconds to Duration/Expiration

[crnbarr93]

Description

We are currently using our Milliseconds struct for both durations and expiration. We should add type aliases for both cases to allow for better schema generation and understanding of what the field is referencing

Implementation

Create two type aliases for Milliseconds:

1. MillisecondsDuration
2. MillisecondsExpiration

Replace references to Milliseconds with the appropriate type.

Acceptance Criteria

All cases of Milliseconds replaced with one of the aliases.