Enable inithist ("i" file writing and reading)

### What is the feature/what would you like to discuss?

Need to implement the capability to read and write the "i" file for hybrid runs in CAM-SIMA.

### Is there anyone in particular you want to be part of this conversation?

_No response_

### Will this change (regression test) answers?

No

### Will you be implementing this enhancement yourself?

Any Software Engineer can do this

The issue names CAM-SIMA, inithist, and the “i” file for hybrid runs but does not identify implementation files or tests. Start by locating the existing hybrid-run initialization and history-file read/write entry points, then trace how an “i” file should be handled. Done means the capability works for hybrid runs and the relevant behavior is verified.

Written by the indexing model from the issue text.