chore: MSRV bump

[toidiu]

Resolved issues:

#1735
#1750
#1751
#1752
#1804
#1991
#1992
#1993

Description of changes:

This PR bumps the MSRV to 1.71.1. It also bumps and unpins many crates that were previously pinned due to a lower MSRV.

Testing:

CI passes

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[toidiu]

We are currently pulling in two different version of aws-lc-syc from s2n-quic-crypto and s2n-tls-sys.

Its possible to fix this by restricting aws-lc-rs version in s2n-quic-crypto or updating the aws-lc-rs in s2n-tls-sys. Ideally we bump version in s2n-tls-sys but need to discuss with team if its possible to do that soon and then do a release of s2n-tls.

[camshaft]

We also need to update the rust-version in all of the Cargo.toml files. This will notify users on older toolchains that it's unsupported.

[camshaft]

This isn't great. It will require us to do the same thing every time aws-lc-sys gets a new minor release. I think either aws-lc-sys also needs to bump to the same major version as aws-lc-rs or aws-lc-rs needs to export the C headers/lib dir so s2n-tls-sys can use it.

[camshaft]

While you're here, we should also do default-features = false

[justsmth]

If you do default-features = false, you will need to add features = ["aws-lc-sys"].

(Consumers will still be able to select the "fips" feature with this. If you use the "non-fips" feature, then "fips" is blocked.)

[camshaft]

Although, thinking about that a bit more, it does mean that if you enable fips that both sys and fips-sys will be built, since we've forced that dependency here. Not sure if there's a way around that, though.