Give the generated handles the pointer boundary a caller can cross

[estebanzimanyi]

WITNESS: the root gomeos package calls 681 distinct MEOS C symbols by hand,
and every one of them already has a wrapper in the generated functions
package -- 3554 wrapped symbols plus 62 #define aliases. The hand-written
package nevertheless imports functions 0 times, and it cannot: a cgo type
belongs to the package that declares it, so this package's *C.Temporal and
the generated package's *C.Temporal are different Go types, and Inner()
returns one of them. Nothing in the generated surface exposes a type both
packages can name.

MEASURED: the emitter gives each opaque handle a Pointer() method and a
<T>FromPointer constructor over unsafe.Pointer, which is the same contract
MEOS.NET's generated handles already carry as IntPtr. Three examples cross the
boundary in both directions: a sequence built here reads back through
TemporalNumInstants and TemporalSubtype as 3 and Sequence; the pointer
compares equal after the round trip, so the handle is carried rather than what
it points at; and TemporalFromPointer(nil) answers a nil handle whose
Pointer() is nil. The suite reads 118 result lines, 0 skipped, against 115
before, and the floor moves with it.

functions/meos_meos_pointcloud.go moves because regeneration takes the
catalog as it stands and MEOS publishes two more point cloud entries than the
committed snapshot carries; the snapshot is a projection, so it follows.

WHY: a binding is a projection of the catalog, and the hand-written package
duplicates 7377 lines of a surface the generator already produces -- including
TBoolValueAtTimestamp, which composes temporal_at_timestamptz with
TBoolStartValue where MEOS publishes tbool_value_at_timestamptz and the
generated package wraps it. Retiring that duplication needs the two packages to
exchange a handle, and the pointer is the only type they can both name. This
adds no signature and removes none.