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Modernizes _to_dict by replacing temporary variables with walrus operator assignments and removing outdated Python 3.7 comments.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