ci: Check MSRV

[pyfisch]

I think it is a good idea to build everything and run the test suite with a matrix of different compilers and features e.g.:

• compiler: MSRV, stable
• features: no default features, default

[waywardmonkeys]

Pull request #28 broke MSRV.

I can bump it here or I can look at reworking things to not require a bump. Let me know.

Also, I've restructured CI in this PR now to handle the additional checks and simplify the CI.

[pyfisch]

I can bump it here or I can look at reworking things to not require a bump. Let me know.

Bump it here to 1.60, thanks.

[waywardmonkeys]

Okay, will take care of both when I am home tonight. On a long weekend in Bangkok at the moment.

[pyfisch]

Resolved by #33

[waywardmonkeys]

Thanks!