LT-22576: Don't allow set phon feats on user-defined NCs

[aror92]

Add method to RuleFormulaControl to check if NC is user-defined.

Update OnDisplayContextSetFeatures in RuleFormulaSlice to display the set phonological features option only if the NC uses features and is not user-defined.

Note: currently there is no way to distinguish user-defined NCs from auto-generated NCs other than the class's name. When we make model changes, we plan to add a flag to track whether a NC is auto-generated, and then the check here can be modified.

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This change is 

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   11m 52s ⏱️ + 1m 2s
5 761 tests ±0  5 680 ✅ ±0  81 💤 ±0  0 ❌ ±0 
5 770 runs  ±0  5 689 ✅ ±0  81 💤 ±0  0 ❌ ±0 

Results for commit 1d6a7c8. ± Comparison against base commit 8dd2468.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.44%. Comparing base (8dd2468) to head (1d6a7c8).

Files with missing lines	Patch %	Lines
Src/LexText/Morphology/RuleFormulaControl.cs	0.00%	7 Missing and 4 partials ⚠️
Src/LexText/Morphology/RuleFormulaSlice.cs	0.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1051   +/-   ##
=======================================
  Coverage   36.43%   36.44%           
=======================================
  Files        1354     1354           
  Lines      295676   295692   +16     
  Branches    40223    40228    +5     
=======================================
+ Hits       107742   107753   +11     
+ Misses     158661   158660    -1     
- Partials    29273    29279    +6     

Files with missing lines	Coverage Δ
Src/LexText/Morphology/RuleFormulaSlice.cs	0.00% <0.00%> (ø)
Src/LexText/Morphology/RuleFormulaControl.cs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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[aror92]

I've had Devin review and have addressed all comments except the following:

Sibling slice still enables a features-related command without the new check
RegRuleFormulaSlice.OnDisplayContextSetVariables (RegRuleFormulaSlice.cs:71) still gates purely on IsFeatsNCContextCurrent. That command sets feature variables rather than feature values, so it may intentionally remain enabled for user-defined classes, but it edits the same shared PhNCFeatures object; worth confirming whether LT-22576 also applies there.

The request in LT-22576 was specifically about the "Set Phonological Features" option, not about set variables. I don't know whether users would want set variables gated similarly as well. I wouldn't make this additional change unless users request it, or unless a human reviewer thinks it is needed.

[aror92]

Unit tests to be added in a separate PR. Danny is kick-starting that for me using Claude (since I don't have a subscription yet), to get all the test set-up out of the way.

[thejambi]

@thejambi reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on aror92).

[thejambi]

@thejambi reviewed 1 file and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on aror92).