Read a geometry and a geography through the HexEWKB reader of each

[estebanzimanyi]

The codec patterns of parser/enrich.py read a hex reader as from_hex?e?wkb and a hex writer as
as_hex?e?wkb, so they take the spelling MEOS gives the functions of the geometries,
geom_from_hexewkb, geog_from_hexewkb and geo_as_hexewkb, beside the _from_hexwkb and _as_hexwkb of
every other type. MobilityDB backs the SQL functions geometryFromHexEWKB(text),
geographyFromHexEWKB(text) and asHexEWKB(geometry|geography, text) with them, so the readers carry
SQL signatures returning geometry and geography, and the class they share, GSERIALIZED, states its
wkb encoding as Set or Temporal states theirs: readers keyed by SQL type, geom_from_hexewkb for
geometry and geog_from_hexewkb for geography, and the one writer geo_as_hexewkb as its wkb
encoder, its endian left NULL, which wkb_variant_from_endian reads as the machine's byte order.
Its text and MF-JSON forms carry no SQL signature, PostGIS owning geometry and geography, and keep
the functions the C shapes give them.

Witness: over MobilityDB master 2d13c5c42d, typeEncodings.GSERIALIZED states
readers.wkb = {geography: geog_from_hexewkb, geometry: geom_from_hexewkb} and
encoders.wkb = geo_as_hexewkb, where it stated no wkb encoding, so a binding reading a codec per
SQL type found none for geometry or geography.

Measured over MobilityDB master 2d13c5c42d, the catalog derived from the installed headers of a
libmeos built by tools/provision-meos.sh, against the catalog the same headers give on master:
GSERIALIZED is the one class whose codec changes; its 473 parameters gain the wkb encoding in
their wire; the three functions are filed under io rather than conversion; nothing else moves.
The suite passes its 497 tests, 25 skipped as on master, tests/test_codecs.py stating the codec on
a synthetic catalog and on the derived one.

Why: one GSERIALIZED stands for two SQL types, so a single decoder cannot tell a binding which of
them a string names; the reader each SQL type's own function provides can, as intset_in and
floatset_in do for Set.