Parity Codec bumps MSRV to 1.64.0

[mriise]

proc-macro-crate (dependency of parity-scale-codec-derive) has no patch number defined for toml_edit which made a recent patch to update winnow which bumps the MSRV.

PR: bkchr/proc-macro-crate#35

[mriise]

This is breaking the new MSRV check in CI for both #304 and #305

[thomaseizinger]

Damn, when will people stop making MSRV breaking changes in patch releases. This makes me wonder whether we should retain parity-scale-codec as a dependency in here.

[thomaseizinger]

I think the way forward here is to document (and test) that the MSRV for multihash only applies with all features disabled. That gives us control over this until we can remove parity-scale-codec from the library.

[vmx]

A MSRV bump was needed due to toml_datetime, which was then merged with #315. Hence I'm closing this issue as we are now at the MSRV of 1.64.