Handle IO for (CLI) morph inputs in a function

[Sparks29032]

CLI morph inputs were handled separately in the single morph and two multiple morph functions within morphapp.py. This has been restructured into a function in morph_io.py. Note that Python-only morphs are still handled separately outside this function as they are not enabled for multiple-morphs/targets (since a user can simply write a for loop instead).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (f5fc9ac) to head (8d2ba97).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #274 +/- ##
=======================================
Coverage 99.92% 99.93% =======================================
Files 24 24 Lines 1398 1446 +48 =======================================
+ Hits 1397 1445 +48 
Misses 1 1 

see 1 file with indirect coverage changes

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[sbillinge]

this looks fine modulo comments. It needs tests for the logic.