C structs

# C's structs (owner, 2026-10-10). One whose fields Zag can spell comes through as a `layout.C struct`
# with C's field names (`tm`, 56 bytes as C lays it out); one Zag never looks inside comes through
# opaque, named as C names it (`FILE`, not the C library's own `__sFILE`), only pointed at:
# `fopen` gives a `ptr.mut[FILE]`, and another struct's pointer handed to `fclose` is refused.
# A field named like a Zag keyword keeps its name after the dot (`'b'.size`); a function so named is
# reached by path (`my.size[…]`).
incl.C.system["time.h", "stdio.h"];
incl.C["headers/shapes.h"];

MAIN {
    let 'b' := buf[size = 42, count = 7];
    std::print.useful["tm is ", size.of[tm], " bytes, buf ", size.of[buf], "; size ", 'b'.size, ", count ", 'b'.count, newln];
}