build: setup msrv and edition consistently in all Cargo.toml

[knutties]

Problem

@SanchithHegde pointed out the missing rust-version and edition values in our crates.

Solution

Set the value in the top-level Cargo.toml and reference it in all the crates.

[ayushjain17]

if I am not wrong, this would get reverted in smithy generation
and I suppose we should use a different value just for the provider, so that we can have a higher inclusion percent

the server can be at a high MSRV like 1.82.0 but the sdk and the provider should not be dependent on this high of a number

[knutties]

This was based on @SanchithHegde's comment using the cargo msrv command (I think uniffi forces it). Running it currently. Will add the output to the PR.

Can we configure smithy to generate this the way we want it? cc: @ShubhranshuSanjeev @ShreyBana

[ayushjain17]

@knutties
smithy-build.json takes minimumSupportedRustVersion as config

[knutties]

➜  superposition git:(fix-msrv) ✗ cargo msrv verify --rust-version 1.81
  [Meta]   cargo-msrv 0.18.4  

Compatibility Check #1: Rust 1.81.0
◝ Rust 1.81.0      Elapsed 2s                                                                                                                                                                                                                                 ◞ Rust 1.81.0      Elapsed 3s                                                                                                                                                                                                                                 ◡ Rust 1.81.0      Elapsed 3s                                                                                                   ◜ Rust 1.81.0      Elapsed 4s                                                                                                         [FAIL]   Is incompatible 

...

uniffi errors

One option is to skip uniffi in rust builds via feature flag (which is actually a good idea by @SanchithHegde). I will do this as well in this PR.

[ayushjain17]

@knutties you would need to check the MSRV for the crate individually I guess
also, uniffi would be needed for the provider only (from the import point of view)

I was thinking something:
sdk and provider to have their respective MSRVs
and all other crates can use a common one from workspace (if at all a common MSRV is needed)

[knutties]

Yes - that is the plan. For crates that wider people have to use - we can lower the msrv - but we will need to remove uniffi dependency in Rust SDKs as it is not needed. uniffi is not needed for the Rust provider - it is needed only in the other language bindings.

We might need some additional CI checks to ensure we compile with some lower msrv as well. I will do that in this PR.

[ayushjain17]

But the rust sdk does not include uniffi