Clippy: Multiple crate versions

Adding

[lints.clippy]
cargo        = { priority = -1, level = "deny" }

to Cargo.toml will also turn on the multiple_crate_versions rule.

It will them complain if the same create was added more than once (with different version numbers) to Cargo.lock.

How could this happen?

What to do about it?

1. We can decide to disregard this rule. Add the following line to Cargo.toml

[lints.clippy]
multiple_crate_versions = "allow"

2. Tell Clippy about the specific crates for which we allow the duplication:

Create the clippy.toml file and add the following entry, with the names of the crates we allow to be duplicated:

allowed-duplicate-crates = [
    "async-channel",
    "event-listener",
    "foldhash",
    "hashbrown",
    "hashlink",
    "wit-bindgen",
]

See allowed-duplicate-crates.

3. Figure out which of our dependencies brought in these dependencies and either replace our own dependencies, or send a Pull-Request to our dependencies to allow for more flexibility.