Add support for query() table function (issue #210)

[nicolas-geysse]

Summary

• Enables DuckPGQ to work with DuckDB's query() table function
• Fixes serialization issues in PathElement, SubPath, and MatchExpression
• Removes unused state management code

Problem

The previous architecture stored MatchExpression in DuckPGQState with an integer index. When query() re-parsed the SQL, the context was different and the expression was lost:

-- This failed before the fix
FROM query('FROM GRAPH_TABLE (pg MATCH (a:Person) COLUMNS (a.id)) tmp');

Solution

Serialize MatchExpression to BLOB directly at parse time in TransformMatch, making the expression self-contained with no dependency on external state. Deserialize from BLOB in MatchBindReplace.

Changes

• TransformMatch: serialize MatchExpression to BLOB at parse time
• MatchBindReplace: deserialize MatchExpression from BLOB
• Fix serialization: PathElement/SubPath now call base class and use property IDs 200+
• Add BOUND_EXPRESSION case in ParsedExpression deserialization
• Fix MatchExpression serialization: call base class, use IDs 200-204
• Cleanup: remove unused transform_expression/match_index from DuckPGQState
• Add test for query() table function

Test plan

• All existing tests pass (126 test cases)
• New test file test/sql/query_table_function.test passes
• Test with basic GRAPH_TABLE in query()
• Test with path patterns in query()

Fixes #210

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