Improve platform testing

[xxxserxxx]

I current have the ability to test Linux, and occasionally OSX. A better solution is needed. I can run a VM on my laptop, but this is not automatable. Ideally, this would be integratable with CI to kick off tests on target platforms:

• Linux
• FreeBSD
• Darwin
• Windows
• OpenBSD
• Other architectures (Linux only)
  • arm64
  • arm7
  • arm6

I've left out a number of permutations and some obvious architectures (386, arm5). While nice to have, they're slowly being phased out by various OSes and I have limited resources to investigating the edge cases.

I would be grateful for suggestions, especially ones that don't require me to incur a new recurring expense -- e.g., I know I can rent a VM from any number of cloud provides and install FreeBSD; this won't scale well for me financially for the number of target platforms, and I'm not even sure such an option is available for OSX.

[xxxserxxx]

I'm tagging this with v4.1.0 not because I expect it to be complete by then, but I'd like to have the low-hanging fruit (Linux) and integrated with CI by then. This should be easy, as it can be done in Github Actions.

[xxxserxxx]

I have a way to test FreeBSD on my laptop, but there's still no CI integration. I believe that I have a solution for Darwin as well, with the same limitation.