Bump MSRV to 1.30.0

We wanted to bump to 1.29 to continue to support mrustc bootstrapping, but on 1.29
there's a bug preventing us from compiling the lightning package only, thus parts
of lightning-net-tokio cause a compilation error.

The advantage of bumping the MSRV is an improved borrow checker which should
enable improved code quality, and not having jump through weird hoops sometimes
to get 1.22 working.