lcg48 refactor

Refactor of functions related to LCG pseudorandom number generation.

Most significantly, pointer arguments are now converted to references rather than the other way around. This has allowed two of the helper functions to become non-unsafe.

In addition, variable naming has been adjusted to align better with the POSIX spec and with Rust types.

src/header/stdlib/lcg48.rs

@@ -41,7 +41,11 @@ pub fn u48_from_ushort_arr3(arr: &[c_ushort; 3]) -> u64 {
 
 /// Make a size-3 array of unsigned short from a 48-bit integer.
 pub fn ushort_arr3_from_u48(value: u64) -> [c_ushort; 3] {
-    [c_ushort::from(value as u16), c_ushort::from((value >> 16) as u16), c_ushort::from((value >> 32) as u16)]
+    [
+        c_ushort::from(value as u16),
+        c_ushort::from((value >> 16) as u16),
+        c_ushort::from((value >> 32) as u16),
+    ]
 }
 
 /// Advances the buffer from the input argument to the next element in