Modernize _delete_entity with Literal typing and f-string formatting

[axif0]

Modernizes _to_dict by replacing temporary variables with walrus operator assignments and removing outdated Python 3.7 comments.

• Replaced content = getattr(...) + if with walrus operator for brevity.
• Removed legacy TODO notes about dropping Python 3.7.
• Improved readability and reduced repetition in both simple and complex property handling.

[PGijsbers]

Thank you! We are currently doing server maintenance so CI/CD might be a bit flaky. Things should stabilize by next week, but we might not be able to merge it before then.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.99%. Comparing base (4b1bdf4) to head (99e3bad).

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #1513       +/-   ##
============================================
- Coverage    79.90%   55.99%   -23.92%     
============================================
  Files           36       36               
  Lines         4349     4347        -2     
============================================
- Hits          3475     2434     -1041     
- Misses         874     1913     +1039     

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