(feature): adds API on Constraint to get var ids

[therapon]

Adds two new methods on Constraint that provide the variables IDs for a constraint

• extend_dependent_variable_ids(self, Extend<Id>). Extends the passed collection to include variable Ids that change the constraint's residual values. Var Ids that affect the constraint only.

• extend_associated_variable_ids(self, Extend<Id>). Extends the passed collection to include variable Ids associated with the constraint--both those that affect the residual and those that do not.

Closes: #234

[codecov]

Codecov Report

❌ Patch coverage is 66.84211% with 63 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.37%. Comparing base (ceba35e) to head (92f1752).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ezpz/src/constraints.rs	66.84%	63 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
- Coverage   90.86%   90.37%   -0.50%     
==========================================
  Files          23       23              
  Lines        5025     5215     +190     
==========================================
+ Hits         4566     4713     +147     
- Misses        459      502      +43     

Flag	Coverage Δ
unittests	90.37% <66.84%> (-0.50%)	⬇️

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[codspeed-hq]

Merging this PR will not alter performance

✅ 8 untouched benchmarks
⏩ 16 skipped benchmarks¹

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_{Comparing tsk-extract-var-ids (92f1752) with main (ceba35e)}

Footnotes

1. 16 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[adamchalmers]

Is this basically going to be computing the exact same data as Constraint::nonzeroes, but collecting into a single collection rather than multiple (row0, row1, row2 etc)?

If so, let's either
A. deduplicate them, so there's only one place that says which IDs can alter the residual
B. Have a property-based test (we use proptest elsewhere in this codebase) that asserts the invariant that extend_dependent_variable_ids should return the same IDs as nonzeroes for any constraint

[therapon]

I am going with B for now and leaving A as a follow up.

For A the the refactor would need an internal helper function that both public APIs will call. I'll make an issue for it.

[therapon]

See #236