I forgot that even on a 64-bit Processor and 64-bit OS, PHP may still be installed as 32-bit.
So we probably have to wait a while until we can realistically make a change.

OR, we could just throw out a warning at installation and say we don't support 32-bit officially and why, but let it continue to work for 99.999% of things.

There's also an issue with 'integer' fields in catalogues.

If a user enters a huge value, PHP will lock it to it's maximum integer size.

However, we are using ints, not bigints, so it overflows trying to save into the DB.

Note that we can use bigints in MySQL even if MySQL is installed as 32 bit. So we don't need to check if MySQL is 64 or 32 bit at all.

Update on this:
- Desktop processors have not been 32-bit for at least 15 years
- ARM is dropping 32-bit support for new CPU designs in 2022
- Windows no longer supports 32-bit installs
- Ubuntu dropped 32-bit library support then back-tracked (so people can run old games)
- Linux Mint dropped 32-bit library support
- Mac migrated ages ago

So to me the only likely situations of running 32 bit would be:
- Older Raspberry Pis running 32-bit ARM chips
- People who weirdly install 32-bit PHP on 64-bit Windows (a build is still provided as of this date)

Probably we can leave this a few more years, we're still 17 years from 2038, so it's still unlikely people are going to use dates that far ahead.

I am thinking about us doing a kind of soft requirement - you can run on 32 bit, but don't expect to create a site on 64 bit and be able to migrate it down to 32.