Restrict swap_rows, hnf, snf to MatElem; to apply to MatRingElem work with underlying matrix

[JohnAAbbott]

Draft because I disabled swap_rows and swap_rows! for MatRingElem (by changing MatrixElem to MatElem, as suggested by @fingolfin in issue #2247 ), as a consequence I also disabled in the same way hnf (several variants) and snf (several variants). I have commented out the corresponding tests -- to state the obvious, these will be removed if the draft becomes a non-draft.
This is obviously a breaking change... so there's no need to state the obvious!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.08%. Comparing base (f9e624d) to head (4943eaa).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2339      +/-   ##
==========================================
- Coverage   88.15%   88.08%   -0.07%     
==========================================
  Files         126      126              
  Lines       32093    32079      -14     
==========================================
- Hits        28290    28258      -32     
- Misses       3803     3821      +18     

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.14%. Comparing base (f9e624d) to head (4943eaa).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2339      +/-   ##
==========================================
- Coverage   88.15%   88.14%   -0.01%     
==========================================
  Files         126      126              
  Lines       32093    32091       -2     
==========================================
- Hits        28290    28288       -2     
  Misses       3803     3803              

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.14%. Comparing base (f9e624d) to head (4943eaa).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2339      +/-   ##
==========================================
- Coverage   88.15%   88.14%   -0.01%     
==========================================
  Files         126      126              
  Lines       32093    32091       -2     
==========================================
- Hits        28290    28288       -2     
  Misses       3803     3803              

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.14%. Comparing base (f9e624d) to head (4207857).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2339      +/-   ##
==========================================
- Coverage   88.15%   88.14%   -0.01%     
==========================================
  Files         126      126              
  Lines       32093    32093              
==========================================
- Hits        28290    28288       -2     
- Misses       3803     3805       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

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

[JohnAAbbott]

Question:
Is the intention that the hnf and snf functions work also with MatRingElem (via simple 1-liner functions)? [if so, then I should re-activate the commented out tests]
And what about swap_rows?

[thofma]

My guess would be that we don't need hnf, snf or swap_rows methods for MatRingElem.

[fingolfin]

No objections to this in triage.