Record the Go signature each generated wrapper is emitted with

[estebanzimanyi]

A caller of a generated wrapper needs the shape the generator CHOSE, and that
shape is not the C parameter list. tbool_value_at_timestamptz declares four C
parameters while the emitted wrapper takes three, folding the bool *value
out-parameter into a second result; an array and its length collapse into one
slice; a char * becomes a string. Anything reading the catalog C signature
to call these wrappers reconstructs a shape they do not have.

SIGNATURES states what the generator emits: each MEOS C name mapped to the Go
name, the parameters and the result types, recorded at the two sites that
assemble a signature. A function absent from it has no wrapper to call, which is
the honest answer rather than a guess.

It is the piece the object layer consumes, so the two generators cannot disagree
about a folded out-parameter -- the same split MEOS.NET keeps between
tools/codegen.py and tools/objectgen.py.

MEASURED: 3562 wrappers emitted, 3562 recorded, so the map is total over the
emitted surface rather than a subset. Regenerating from one catalog with and
without this commit yields 15 files on each side and a diff of 0 lines over
41653 lines of generated Go, so the emitted package does not move. The baseline
run carries no SIGNATURES attribute, which is what makes it a control rather
than a second run of the same code.

The change is confined to the Python generator and its Go output is
byte-identical, so it carries no compilable change.