chore: delete IsLastLID

[cheb0]

Description

It's easier to just use a new Source interface to iterate over all postings in index analyzer

---

• I have read and followed all requirements in CONTRIBUTING.md;
• I used LLM/AI assistance to make this pull request;

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.63%. Comparing base (4ad8f17) to head (5be2437).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/index_analyzer/main.go	0.00%	43 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #469      +/-   ##
==========================================
+ Coverage   70.44%   70.63%   +0.18%     
==========================================
  Files         232      232              
  Lines       18371    18319      -52     
==========================================
- Hits        12942    12939       -3     
+ Misses       4453     4402      -51     
- Partials      976      978       +2     

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[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
Click on Show table button to see full list of degraded benchmarks.

Show table

Name	Previous	Current	Ratio	Verdict
Indexer-4	4ad8f1	6ace8f
	677543019.00 B/op	756189101.00 B/op	1.12	🔴