all: change optional to result in most of the libraries (#16123)

vlib/crypto/rand/rand_openbsd.c.v

@@ -9,7 +9,7 @@ module rand
 fn C.arc4random_buf(p &byte, n usize)
 
 // read returns an array of `bytes_needed` random bytes read from the OS.
-pub fn read(bytes_needed int) ?[]u8 {
+pub fn read(bytes_needed int) ![]u8 {
 	mut buffer := unsafe { malloc_noscan(bytes_needed) }
 	C.arc4random_buf(buffer, bytes_needed)
 	return unsafe { buffer.vbytes(bytes_needed) }