Stdlib:
- `format` / `print` in std.sx — both move from `args: ..Any` to
`..args: []Any`. The post-issue-0049 lowering makes this safe
across module boundaries.
- `open` in fs.sx — `args: ..s32` → `..args: []s32`. Foreign
C-variadic semantics are preserved (the trailing `, ...` lands
in the generated `declare` regardless of which surface form is
used).
Examples:
- `19-varargs.sx` — `sum` / `print_all` migrated.
- `20-any-varargs.sx` — `print_any` / `count` migrated.
- `50-smoke.sx` — `typed_sum` migrated.
- `120-interp-variadic-any.sx` — comment-only update referencing
the new form.
- `ffi-foreign-cvariadic.sx` — three C-variadic foreign decls
migrated; header comment refreshed.
Suite stays at 214/214. The legacy `name: ..T` surface form is
still accepted by the parser; rejection follows in a later commit
once specs.md catches up.
5b3d86440b