refactor(query): decouple logical optimization from physical planning

[forsaken628]

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Summary

Previously, a single SExpr representation and SExpr → SExpr optimizer interface tied frontend logical rewrites to CBO and physical-plan finalization. Logical semantics and execution-stage concerns shared the same
contract, making maintenance difficult and constraining how CBO could evolve to model physical implementations.

This PR separates those stages without changing the existing search and costing algorithms:

• Keep the frontend optimizer pipeline on logical SExpr, and introduce a separate physical-planning entry that consumes SExpr and produces PExpr.
• Share expression structure, traversal, and validation through a generic skeleton, while keeping logical and physical state and invalidation policies distinct.
• Migrate physical rewrites and execution-plan builders to PExpr, with no reverse conversion to SExpr.
• Prepare Mutation inputs and decorrelate INSERT WHEN subqueries before physical planning, rather than modifying logical structure after selection.
• Handle physical EvalScalar cleanup independently and remove unused Memo collection from the logical pipeline.
• Read lineage for planned statements from binding-time snapshots.

This establishes an independently evolvable physical representation. It does not yet introduce new physical implementation alternatives or change the CBO cost model.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

AI assistance

• AI usage: AI assistance was used for implementation, refactoring, review, and validation.
• Responsible human: @forsaken628
• The responsible human has read every line of this diff and can explain each change

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