fix(unparser): Fix column alias rewriting for Filter nodes preserved by Inexact filter pushdown

[sgrebnov]

Which issue does this PR close?

N/A

PR improves the unparser to handle plans where a Filter node is preserved above a TableScan with pushed-down filters — either because supports_filters_pushdown returns Inexact/Unsupported, or because the plan was constructed manually.

Rationale for this change

When supports_filters_pushdown returns Inexact, the optimizer preserves a Filter node above the TableScan. The unparser's unparse_table_scan_pushdown only handled TableScan, SubqueryAlias, and Projection nodes — it did not handle this SubqueryAlias(Filter(TableScan)) shape, producing wrong column references and lost projections in the generated SQL.

Additionally, try_transform_to_simple_table_scan_with_filters (used by the JOIN handler) collected Filter node predicates without alias rewriting, while TableScan filters were rewritten. This caused duplicate un-aliased predicates in JOIN ON clauses (e.g. nation.n_name instead of n1.n_name), producing invalid SQL for queries like TPC-H Q7.

Example 1:

Before (incorrect):

SELECT * FROM nation AS n1 WHERE (nation.n_name = 'FRANCE') AND (nation.n_name = 'FRANCE')

After (correct):

SELECT n1.n_nationkey, n1.n_name FROM nation AS n1 WHERE (n1.n_name = 'FRANCE') AND (n1.n_name = 'FRANCE')

Example 2:

Before (JOIN, incorrect — fails with "No field named nation.n_name"):

... INNER JOIN nation AS n1 ON (supplier.s_nationkey = n1.n_nationkey)
  AND ((n1.n_name = 'FRANCE') OR (n1.n_name = 'GERMANY'))
  AND ((nation.n_name = 'FRANCE') OR (nation.n_name = 'GERMANY'))

After (JOIN, correct — deduplicated):

... INNER JOIN nation AS n1 ON (supplier.s_nationkey = n1.n_nationkey)
  AND ((n1.n_name = 'FRANCE') OR (n1.n_name = 'GERMANY'))

Filters duplicated between the Filter node and TableScan.filters (common with Inexact pushdown) appear redundantly in the generated SQL. No optimization currently exists to detect and remove these duplicates in that path. This does not affect query correctness and can be optimized separately.

What changes are included in this PR?

1. Add a LogicalPlan::Filter arm to unparse_table_scan_pushdown — recurse through the filter to the TableScan, then rewrite the filter predicate's column references to use the alias via TableAliasRewriter. Skip predicates containing subquery expressions (Exists/InSubquery/ScalarSubquery) since TableAliasRewriter cannot rewrite OuterReferenceColumn inside subquery LogicalPlans — returning None falls back to wrapping the plan as a derived table, preserving the original table name for outer references.

2. In try_transform_to_simple_table_scan_with_filters, rewrite already-collected Filter node predicates with TableAliasRewriter before deduplicating against rewritten TableScan filters.

Are these changes tested?

Yes. Added 4 regression tests and also verified end-to-end with all 22 TPC-H queries against a TableProvider returning Inexact for supports_filters_pushdown.

Are there any user-facing changes?

No API changes. The unparser now generates correct SQL for SubqueryAlias(Filter(TableScan)) and Filter(TableScan) plans produced by Inexact filter pushdown or constructed manually, including correct column alias rewriting and filter deduplication in JOINs.