Avoid 64-bit math for remainders.
Avoid 64-bit math for remainders.

This improves MSVC x86 perf by 2.1% and doesn't affect other platforms.

The early truncation technique was described here:

```
static inline uint32_t mod1e9(const uint64_t x) {
  // Avoid 64-bit math as much as possible.
  // Returning (uint32_t) (x - 1000000000 * div1e9(x)) would
  // perform 32x64-bit multiplication and 64-bit subtraction.
  // x and 1000000000 * div1e9(x) are guaranteed to differ by
  // less than 10^9, so their highest 32 bits must be identical,
  // so we can truncate both sides to uint32_t before subtracting.
  // We can also simplify (uint32_t) (1000000000 * div1e9(x)).
  // We can truncate before multiplying instead of after, as multiplying
  // the highest 32 bits of div1e9(x) can't affect the lowest 32 bits.
  return ((uint32_t) x) - 1000000000 * ((uint32_t) div1e9(x));
}
```

ulfjack/ryu,ulfjack/ryu,ulfjack/ryu,ulfjack/ryu