Make code compile and lint cleanly under all relevant versions of rust

[jlapeyre]

We need to have more reliable CI for all relevant versions of the rust toolchain. Is there a way to make this happen? I'd prefer to not to commit Cargo.lock.

In our GH CI, this is what runs with the default Rust version (is it maybe the latest stable?)

openqasm3_parser/.github/workflows/main.yml

Lines 26 to 29 in 5305ac3

	- name: Clippy
	run: cargo clippy --all-targets -- -D warnings -D clippy::dbg_macro
	- name: Run tests
	run: cargo test --verbose -- --skip sourcegen_ast --skip sourcegen_ast_nodes

But for the MSRV, we do not run clippy in CI, and the command for running tests is slightly different.

openqasm3_parser/.github/workflows/main.yml

Lines 41 to 44 in 5305ac3

	- name: Build
	run: cargo build --release --verbose
	- name: Run tests
	run: cargo test --verbose --lib --tests -- --skip sourcegen_ast --skip sourcegen_ast_nodes

I found that occasionally upon pushing a PR, CI would fail because some component or dep is upgraded.

I tried some conditional compilation. For example here:

openqasm3_parser/crates/oq3_syntax/src/ptr.rs

Lines 34 to 49 in 5305ac3

	impl<N: AstNode> Clone for AstPtr<N> {
	#[rustversion::before(1.74)]
	fn clone(&self) -> AstPtr<N> {
	AstPtr {
	raw: self.raw.clone(),
	_ty: PhantomData,
	}
	}
	#[rustversion::since(1.74)]
	fn clone(&self) -> AstPtr<N> {
	AstPtr {
	raw: self.raw,
	_ty: PhantomData,
	}
	}
	}

I think it helped, but I don't recall why I was not able to solve the problem completely.

[Raghav-Bell]

Followings are good references to resolve this issue:
clone_copy issue reported
[Roadmap] Lint groups
Thanks