[antonsoo]

Component reads and failed removals can create empty registry rows. Clearing tags also recreates an empty row when checking its loop condition. These rows keep otherwise unused entities alive, and the empty tag rows enter saved games.

Use non-inserting lookups and remove empty rows during cleanup. Live references and incoming relations still retain their entities; query results and the save schema are preserved. This follows the lifetime behavior explained in #9.

Validation:

• All ten lifetime regressions fail before and pass after. Full tests pass on Python 3.10 and 3.12: 106 passes, with the same two pickle XPASS cases as unchanged main. Mypy and Ruff pass.
• Across 24 inventory-loop configurations, 4,352 consumed items and their empty saved records are released. Hit-point histories and query results are unchanged; the largest tested save drops from 8,026 to 334 bytes.
• A save produced on main loads under this repair and its empty item record can be cleared. Repaired saves also load under unchanged main.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.18%. Comparing base (7e852c0) to head (28fa94d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
+ Coverage   99.17%   99.18%   +0.01%     
==========================================
  Files           9        9              
  Lines         966      981      +15     
==========================================
+ Hits          958      973      +15     
  Misses          8        8              

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[HexDecimal]

These fixes are good, but this PR seems to showcase an architectural issue with the existing code. It appears that defaultdict is causing more problems than it solves.

I'll approve this with some minor changes.