:sig
u64 file_write(u64 h, String data)

:params
h : handle from file_open() opened for writing
data : bytes to write at the current offset
return value : number of bytes written

:content
Writes `data` at the handle's current offset and advances the offset. The handle must come from `file_open()` with a writable mode (`"w"`, `"a"`, or `"r+"`). Binary-safe: `data` may contain NUL and other non-text bytes.

:example
u64 h = file_open("/tmp/doc-write.txt", "w");
u64 n = file_write(h, "hello world");
file_close(h);
print(n, " bytes -> ", file_get_contents("/tmp/doc-write.txt"), "\n");

:see
>sys
file_open
file_pwrite
file_read
file_close