🔨 Introduce FASTFLOAT_INSTALL to make install optional
🔨 Introduce FASTFLOAT_INSTALL to make install optional

When using fast_float as a PRIVATE dependency, it is not required to install it.
This flag give user using fastfloat with add_subdirectory the opportunity to disable install target
Default behavior is conserved since FASTFLOAT_INSTALL is ON

fastfloat/fast_float,fastfloat/fast_float,fastfloat/fast_float,fastfloat/fast_float