Carry a MEOS struct that is all scalars as a value

[estebanzimanyi]

A struct MEOS hands over through a pointer is not always opaque. Where the
catalog states its whole layout in scalars and no class stands for it, the
address carries nothing the value does not: Interval, Match, BOX3D,
AFFINE and TimeTzADT are values, and the binding carries them as such. The
argument sites take the value and hand MEOS the address of a copy that lives
exactly as long as the call; the return sites read the value MEOS wrote and
leave the memory to MEOS, as every other value the layer reads back does. 49
methods reach the object layer that way — TsTzSpan.Duration,
Span.ShiftScale, Temporal.Tprecision, TsTzSpanSet.Bins,
Temporal.FrechetPath and their kin — 1171 methods against 1122, 124 deferred
against 171.

A value struct reads and writes itself through the text I/O the catalog names
for it, so Interval.In("1 day") goes through MEOS's own parser and
ToString() through its printer, at the decimal digits the catalog's encoding
records. Nothing about the format is stated twice.

The rule excludes a struct a class already stands for, which is what keeps
Npoint and Nsegment one type each rather than a class and a struct spelling
the same value.

Four tests read the values back: a span answers its duration as an interval of
2 days, an interval round-trips its own text and raises on text MEOS refuses, a
span shifted and scaled by two intervals given as values lands where it should,
and a Frechet path arrives as the matches themselves — in the order the kernel
walks its distance matrix, from the last pair back to the first.