fix: Fix pushdown conjuncts instead of generating join columns

[MBkkt]

Adjust how do we pushdown and place conjuncts (filter expressions/predicates) instead of generate join columns.
"join columns" is design decision with different flaws:

1. it forces projection to be created right after join (so it can be project earlier than needed)
2. join columns will be projected separately from expressions where they used (so it can be unnecessary columns and project operations)
3. it requires to write code in each join method
4. it's probably slower, because a lot of allocations in this algorithm (in query graph and plan enumeration)

[Copilot]

Pull Request Overview

This PR refactors the join optimization strategy by removing the "join columns" approach in favor of pushing down filter conjuncts (predicates). The change eliminates unnecessary projections and simplifies the join implementation.

Key Changes:

• Removed join column generation logic and replaced it with direct conjunct pushdown
• Refactored extractNonInnerJoinEqualities to return the left table and handle both single-table and multi-table cases
• Simplified join edge logic by removing leftColumns/rightColumns vectors and their associated expressions
• Modified join placement to handle filter pushdown based on join optionality

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
axiom/optimizer/tests/JoinTest.cpp	Updated test expectations to reflect new behavior where right joins convert to left joins and projections are removed
axiom/optimizer/tests/DerivedTablePrinterTest.cpp	Fixed aggregate expression to use correct table reference (t3.y instead of dt1.y)
axiom/optimizer/tests/CMakeLists.txt	Removed JoinTest.cpp from build configuration
axiom/optimizer/ToGraph.h	Renamed translateJoin to addJoin and removed addJoinColumns helper method
axiom/optimizer/ToGraph.cpp	Refactored join translation logic to use conjunct pushdown instead of join columns
axiom/optimizer/QueryGraph.h	Removed join column vectors and simplified join edge logic with updated isInner/isNonCommutative checks
axiom/optimizer/QueryGraph.cpp	Fixed typo ('outr' → 'outer'), cleaned up template usage, and updated function signatures
axiom/optimizer/PlanObject.h	Added null pointer checks to PlanObjectSet methods
axiom/optimizer/Plan.cpp	Removed join column expressions from downstream column tracking
axiom/optimizer/Optimization.h	Renamed placeConjuncts parameter from allowNondeterministic to joinsPlaced
axiom/optimizer/Optimization.cpp	Removed ProjectionBuilder and join column mapping logic, simplified join construction
axiom/optimizer/DerivedTable.cpp	Added logic to prevent pushdown to optional sides of joins during conjunct distribution

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[MBkkt]

it is written twice in the current main