refactor: remove table scan restriction

[stuarttimwhite]

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Rationale for this change

We unnecessarily restrict to table scans for aggregation.

What changes are included in this PR?

Remove table scan restriction in aggregate_to_proof_plan

Are these changes tested?

Yes

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.70%. Comparing base (32155a9) to head (786417a).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/proof-of-sql-planner/src/plan.rs	88.88%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1097      +/-   ##
==========================================
- Coverage   96.71%   96.70%   -0.01%     
==========================================
  Files         302      302              
  Lines       58947    58918      -29     
==========================================
- Hits        57008    56979      -29     
  Misses       1939     1939              

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[github-actions]

🎉 This PR is included in version 0.127.18 🎉

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