Consolidate filter classification into physical planner

[adriangb]

Which issue does this PR close?

Related to:

• Unified TableScan.filters #19894 - Unified TableScan.filters representation
• UPDATE ...FROM bug #19950 - UPDATE ...FROM bug (filter extraction improvements)
• refactor: Change TableScan.projection from indices to expressions #20091 - Complementary work on consolidated TableScan representation (projections as expressions)

Rationale

Currently, the optimizer calls supports_filters_pushdown() to classify filters during logical optimization. This results in a split representation where:

• Exact/Inexact filters go to TableScan.filters
• Unsupported/Inexact/Volatile filters stay as Filter nodes above the scan

This creates several problems (as described in #19894):

• Filter duplication risk: The same predicate may exist in both a Filter node and TableScan.filters
• Semantic confusion: Unclear which filters are "pushed down" vs. "logical"
• Implementation burden: DML operations must collect filters from multiple locations
• Multi-table safety hazards: UPDATE...FROM scenarios become fragile

What changes are included in this PR?

This PR moves ALL filter expressions to TableScan.filters during logical optimization, deferring classification (Exact/Inexact/Unsupported) to the physical planner.

Changes to push_down_filter.rs:

• Simplified TableScan case to push ALL filters (except scalar subqueries) to TableScan.filters
• Removed filter classification logic (now handled by physical planner)

Changes to physical_planner.rs:

• Enhanced TableScan handler to:
  • Classify filters using supports_filters_pushdown()
  • Create FilterExec for Unsupported/Inexact/Volatile filters
  • Handle projection expansion when filters need columns not in user's projection
  • Apply limits correctly when post-filtering is needed
• Added compute_scan_projection_with_filters() helper
• Added create_filter_exec() helper with async UDF support
• Updated extract_dml_filters() to also extract from TableScan.filters

Behavior Changes:

1. Logical Plan: All filters (except scalar subqueries) now appear in TableScan.filters instead of as separate Filter nodes
2. Physical Plan: The physical planner creates FilterExec nodes for Unsupported/Inexact/Volatile filters
3. Projection Handling: When post-scan filters need columns not in the user's projection, we expand the scan projection and add a final ProjectionExec to trim extra columns

Are these changes tested?

Yes - updated existing tests to match new plan representations:

• Optimizer tests (snapshot updates)
• Physical planner tests
• Core integration tests
• Dataframe and view tests

Are there any user-facing changes?

Plan output changes: Users will see filters in TableScan with partial_filters= or unsupported_filters= annotations in logical plans, rather than separate Filter: nodes. Physical plans remain functionally equivalent with FilterExec nodes where needed.

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