fix: relax MSRV to 1.63

[tottoto]

Resolves #785. Relaxes MSRV to 1.63 from 1.64.

[paolobarbolini]

Considering that the published crate gets the Cargo.toml flattened I wander if the MSRV is already 1.63 without this PR 🤔. See https://docs.rs/crate/tower/0.5.1/source/Cargo.toml

[jplatte]

This effectively reverts #778. Is there a reason you chose to do that instead of fixing #785 the "obvious" way, by updating the changelog?

[tottoto]

I'm not sure what is the obvious way, but the reason is hyper-util's MSRV is 1.63 and tower doesn't use any 1.64 features other than workspace inheritance. As I think maintaining support for older versions of Rust incurs a certain cost, if this does not conform to tower's policy, I will withdraw this proposal.

[jplatte]

I don't have a strong opinion on this one way or the other, let's see what Sean says in hyperium/hyper-util#144.

[paolobarbolini]

Isn't the MSRV effectively 1.63 once the crate is published? I'd expect a cargo version not aware of workspace dependencies to still be able to parse this https://docs.rs/crate/tower/0.5.1/source/Cargo.toml

[jplatte]

That's a good point...