stdlib: print/io of a non-UTF-8 binary raises where PUC-Lua writes raw bytes #409

Found during automated differential review of PR #406 (not caused by it).

print (and io writes) of a binary that is not valid UTF-8 raises Lua.RuntimeException (:io.put_chars argument error) where PUC-Lua 5.3 writes the raw bytes:

print(("日本"):gsub("^.", "X"))  -- crashes; the gsub result itself is byte-identical to PUC

Lua strings are byte strings; any byte-slicing produces non-UTF-8 binaries routinely, so this affects ordinary programs. Likely fix: write via IO.binwrite/latin1-safe path instead of :io.put_chars with unicode translation.

🤖 Filed from an automated review pass.