schemaview.py: minor reorg and test reorganisation

[ialarmedalien]

Note: base branch is the branch in #476 -- that PR should be reviewed and merged first.

Some cut-n-pastage to group relevant methods and tests together in schemaview.py and its test file. Both of these moves were straight cut and paste with no edits.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.10%. Comparing base (2fe479e) to head (f346240).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #477   +/-   ##
=======================================
  Coverage   78.10%   78.10%           
=======================================
  Files          52       52           
  Lines        4512     4512           
  Branches      983      983           
=======================================
  Hits         3524     3524           
  Misses        769      769           
  Partials      219      219           

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[Silvanoc]

Confirmed that only code blocks have been moved.

Just in case anyone else wants to review it too git diff --color-moved is your friend for this task 😉