feat(queryopt): absorption-idempotency optimizer

[jzelinskie]

Description

This PR implements a new optimizer pass that canonicalizes the structure of union expressions according two to laws from set theory: idempotency (A ∪ A = A) and absorption (A ∪ (A ∩ B) = A).

Caveats are treated as opaque structural units: A ∪ Caveat(A) is not simplified, but A ∪ (A ∩ Caveat(B)) = A because A appears as a direct factor.

Arrows are treated as opaque structural units: (A->B) ∪ (A->B ∩ C) = A->B, but (A->B) ∪ (A->C) is not simplified.

This must run after caveat pushdown so it sees the final caveat shape and before reachability-pruning so pruning works on a smaller tree.

Testing

Added unit tests, but also ran the full test suite. LMK if I need to add any other kind of tests when adding optimizers

References

• Wikipedia for set theory absorption

[codecov]

Codecov Report

❌ Patch coverage is 93.97590% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.69%. Comparing base (3263d73) to head (6e45bdc).

Files with missing lines	Patch %	Lines
pkg/query/queryopt/absorption.go	93.83%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3051      +/-   ##
==========================================
+ Coverage   73.64%   73.69%   +0.06%     
==========================================
  Files         499      500       +1     
  Lines       60165    60248      +83     
==========================================
+ Hits        44301    44393      +92     
+ Misses      12674    12666       -8     
+ Partials     3190     3189       -1     

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