compiler: Tweak use of degenerating_indices when determining iteration directions

[EdCaunt]

Tweaking the logic for treatment of degenerating indices created through Buffer(1) made the time loop direction default to forward in setups where it shouldn't. This hotfix should correct this behaviour and introduces additional checks for this.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.06%. Comparing base (805394b) to head (5326df0).

Files with missing lines	Patch %	Lines
tests/test_mpi.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2873   +/-   ##
=======================================
  Coverage   79.05%   79.06%           
=======================================
  Files         248      248           
  Lines       51252    51276   +24     
  Branches     4428     4431    +3     
=======================================
+ Hits        40518    40539   +21     
- Misses       9924     9927    +3     
  Partials      810      810           

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