[core] Directly index the array of Squares with a given index

In Square::from_index_unchecked, instead of using TryFrom to convert the index
to a square, just index directly into the Square::ALL array. This function is
already marked unsafe.

core/src/coordinates.rs

@@ -115,7 +115,9 @@ macro_rules! range_bound_struct {
 
 coordinate_enum!(
     Direction,
-    [North, NorthEast, East, SouthEast, South, SouthWest, West, NorthWest]
+    [
+        North, NorthEast, East, SouthEast, South, SouthWest, West, NorthWest
+    ]
 );
 
 impl Direction {
@@ -262,7 +264,7 @@ impl Square {
     #[must_use]
     pub unsafe fn from_index_unchecked(x: u8) -> Square {
         debug_assert!((x as usize) < Self::NUM);
-        Self::try_from(x).unwrap_unchecked()
+        Self::ALL[x as usize]
     }
 
     #[inline]