gh-61103: Support float and long double complex types in ctypes module (#121248)

gh-61103: Support float and long double complex types in ctypes module (#121248)

This amends 6988ff02a5: memory allocation for
stginfo->ffi_type_pointer.elements in PyCSimpleType_init() should be
more generic (perhaps someday fmt->pffi_type->elements will be not a
two-elements array).

It should finally resolve #61103.

Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>