Set installed toolchain as default and bump MSRV to 1.77

[wiktor-k]

The docs for the action indicate that unless specified the toolchain will not be used by default.

[wiktor-k]

Hmm... okay, fixing this uncovered another issue: the bindings are using std::mem::offset_of which, according to docs was introduced in Rust 1.77.

Do you think we should upgrade our MSRV or rather find a way to generate sources without offset_of or something else entirely? 🤔

Apparently it is possible to set Rust target when generating bindings: rust-lang/rust-bindgen#2960 (comment)

CC @Jakuje @hug-dev

[Jakuje]

Hmm... okay, fixing this uncovered another issue: the bindings are using std::mem::offset_of which, according to docs was introduced in Rust 1.77.

Do you think we should upgrade our MSRV or rather find a way to generate sources without offset_of or something else entirely? 🤔

Apparently it is possible to set Rust target when generating bindings: rust-lang/rust-bindgen#2960 (comment)

CC @Jakuje @hug-dev

I do not have much experience or overview what all implications of bumping MSRV are, but given that this was here for quite some time and only now somebody noticed, I would say lets bump it. Sounds like there is really not a huge interest in old rust versions in there.

From technical point of view, do we know what is the alternative generated with bindgen set with rust_target < 1.77? Does it just use the experimental naming of the offset_of? Or does it use some different approach? Does it have some performance/readability/usabliity implications?

[Jakuje]

no concerns here

[wiktor-k]

Thanks 👋 . Let's wait for @hug-dev since he touched these parts previously and may have valuable input.

[hug-dev]

Checking at Rust packages in Ubuntu, seems like 1.77 is available on old distributions too so I think we can go with it!

[hug-dev]

Thanks! I am thinking that we could as well write what the MSRV is somewhere in a README! Unneeded as the rust-version field conveys exactly that information