Consistent Integer Types

example of using, to avoid mixed usage of std::uint/std::int and uint/int...
```cpp
using u64 = std::uint64_t;
using u32 = std::uint32_t;
using u16 = std::uint16_t;
using u8  = std::uint8_t;

using i64 = std::int64_t;
using i32 = std::int32_t;
using i16 = std::int16_t;
using i8  = std::int8_t;

using usize = std::size_t;
using isize = std::ptrdiff_t;

#if defined(__GNUC__) && defined(IS_64BIT)
__extension__ using u128 = unsigned __int128;
__extension__ using i128 = signed __int128;
#endif
```

closes https://github.com/official-stockfish/Stockfish/pull/6874

No functional change

src/movegen.cpp

@@ -108,7 +108,7 @@ splat_precomputed_moves(Move* moveList, Square from, Bitboard occupied, Bitboard
     static_assert(Pt != QUEEN && Pt != PAWN, "Unsupported piece type");
 
     // The nth bit in the mask corresponds to the nth square in the piece's pseudo-attacks
-    uint32_t mask;
+    u32 mask;
     if constexpr (Pt == BISHOP || Pt == ROOK)
     {
         const Attacks::Magic& magic = Attacks::magic(from, Pt);