Writing a float does not compile on 32-bit target because of x64-only intrinsic

MSVC, 32-bit target. Serializing a very simple struct with two floats (x/y); reading compiles fine, write fails - to_chars implementation uses `_mm_cvtsi128_si64` intrinsic, which apparently is only defined for 64-bit targets. (zmij.hpp, L759). Workaround is `#define ZMIJ_USE_SIMD 0`, official SIMD-disable define (GLZ_DISABLE_SIMD) is ignored.