refactor time_interp test to fix CI failures

[rem1776]

Description
This just refactors one of the tests so that the input files are created by a separate executable, instead of being written and later read in by the same program. I think this should fix CI failures that pop up from time to time, seems like it hits some kind of race condition and the test hangs but only occasionally.

I also included a small fix for the cmake build to better handle the oversubscribe flag. Now it will do some checks to see if its needed instead of using it automatically using it since that can give errors.

Fixes #1862

How Has This Been Tested?
Tested with intel 2026.1 on the amd box with both build systems

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes