TST: Turn all unhandle warnings into exceptions

[pllim]

While looking at RT run log (e.g., https://github.com/spacetelescope/RegressionTests/actions/runs/18195096489/job/51799323969), I see a lot of warnings (2934 warnings to be precise).

These warnings should be fixed.

And then, the pytest setting should be changed such that any unhandled warning is turned into exception, so it would block testing until the warning is addressed.

[stscijgbot-hstdp]

This issue is tracked on JIRA as HLA-1560.