[estebanzimanyi]

Call a writer with the out-parameters its catalog entry states

CtypesEngine.encode calls a writer with its own signature: every out-parameter the
catalog lists in the writer's shape.outParams gets a slot of its own at its position,
the trailing inputs fill the other positions in order, and a writer handing back its
size in a size_t * is read for that many bytes, less the terminating NUL MEOS counts in
the size of a string. The server reads each writer's out-parameters from the catalog
(writer_outparams) and states them in the route as encode_outparams, beside
encode_aux, for a result, an out-parameter result and the elements of an array result.
set_as_hexwkb, span_as_hexwkb, spanset_as_hexwkb and raster_as_hexwkb, the writers of
459 results on the wire over the catalog of MobilityDB master 1ff2270f7f, are called
with their size_t *size_out; no reader on the wire has an out-parameter.

Witness: tests/test_engine_integration.py, an intset, an intspan and a tint written by
set_as_hexwkb, span_as_hexwkb and temporal_as_hexwkb through CtypesEngine.encode and
read back to their value, and tests/test_server.py, the route of a result whose writer
states size_out and the call the engine receives; both fail on master's server.

Why: the encode a route names for a Set, a Span, a SpanSet or a Raster called the hex
writer with its value and its variant and no size_out, leaving MEOS to write the size
through whatever the third argument register held.

Measured: the 632 tests pass, master's 630 and the 2 above, with libmeos built from
MobilityDB master 1ff2270f7f.

Derive the validated OpenAPI catalog through provision-meos.sh

openapi-validate.yml regenerates the catalog with tools/provision-meos.sh over the
MobilityDB checkout, which runs run.py with MDB_SRC_ROOT naming it, so the @InGroup groups
that make a function public are attached and the exposable functions are projected. The
workflow refuses a document with no path, and a change to provision-meos.sh runs it.

Why: IO-B1 of IO-PLAN.md in MobilityDB #2861. run.py reads the groups from MDB_SRC_ROOT,
else from ./_mobilitydb; the workflow set neither, so every function read internal and
run 41207016338 published a valid document of 0 paths ("Done: 6073 functions (0
stateless-exposable)", "0 paths, 0 schemas").

Measured: over MobilityDB master 1ff2270f7f, run.py over the source headers without
MDB_SRC_ROOT states all 6077 functions internal, 0 exposable, and generate_openapi.py
projects 0 paths; through provision-meos.sh the catalog states 3614 exposable functions
and the document, valid OpenAPI 3.1, 3614 paths and 35 schemas. The check refuses the
document of 0 paths.