Attach the SQL-facing return type from the CREATE FUNCTION signatures

[estebanzimanyi]

Summary

Extends the SQL-facing signature attachment (which already gives each catalog function its sqlArity/sqlArityMax from the CREATE FUNCTION signatures) to also attach the SQL return type.

For the polymorphic Temporal *-returning functions the C signature is a bare Temporal *, which loses the concrete SQL subtype. A binding generator therefore cannot render the result type and must hand-special-case each one — against the single-source/zero-hand-case north star. Examples: getX/azimuth/speed → tfloat, tDwithin → tbool, centroid → tgeompoint (or tgeogpoint for temporal geographies).

Change

parser/sqlfn.py — in _wrapper_sql_sigs, parse the RETURNS <type> clause from the same CREATE FUNCTION name(args) RETURNS <type> AS 'MODULE_PATHNAME','<Wrapper>' statement already scanned for arity (it sits between the arg-list close and the AS), keyed by the wrapper. attach_sqlfn_map then attaches per function:

• sqlReturnType — when the wrapper has a single SQL return type;
• sqlReturnTypeAll — the sorted set when overloads legitimately differ (input-polymorphic wrappers: centroid → {tgeompoint, tgeogpoint}, abs → {tint, tfloat}, atValues → all subtypes).

The CREATE FUNCTION statement is the SoT; nothing is inferred from symbol names.

Effect

287 polymorphic Temporal * C-returns now carry a concrete SQL subtype in the catalog, so every binding (PyMEOS/JMEOS/MobilityDuck/Spark) can generate them without hand subtype maps.

Testing

All 147 parser tests pass (14 skipped); the existing sqlArity/sqlArityMax attachment is unchanged (temporal_as_hexwkb still (1, 2)).