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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[sbillinge]

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