Scan pgtypes sources for out-param Doxygen and step over preprocessor guards

[estebanzimanyi]

The vendored PostgreSQL base-type layer (json, date/interval, …) lives in the sibling pgtypes/ tree, outside meos/, and its base functions carry their @param[out] tags on the .c definitions there — for example json_array_elements in pgtypes/utils/jsonfuncs.c. Two things keep those out-params out of the catalog:

• the out-param Doxygen scan in parser/outparam.py globs only meos/src + meos/include;
• the function-definition regex does not step over the #if MEOS guard that separates a base function's doc block from its definition.

As a result shape.outParams is empty for the whole vendored-base surface, and every binding leaves those out-parameters as visible caller arguments instead of folding them.

This scans pgtypes/**/*.c alongside meos/, and skips a run of blank and preprocessor lines before the return-type line. The skip pattern is a line-based subset of doxygroup.py's _SKIP (which already scans pgtypes for @ingroup): the multi-line-comment alternative is deliberately omitted here because, combined with this module's whole-doc-block match, a DOTALL run inside the skip backtracks catastrophically — doxygroup can afford it because it runs a bounded two-step search.

Adds tests/test_outparam.py covering the plain meos/src case, the guarded pgtypes twin, the sibling-tree scan, and the non-const-pointer cross-check. Regenerating the catalog now marks e.g. json_array_elements → outParams: ['count']; the meos/src surface is unchanged (the skip matches zero lines when there is no guard).