deps: delete the unused workspace dependencies and fix the wit-bindgen hoist

[mfw78]

Delete the workspace dependencies nothing uses, and fix a hoist whose invariant does not hold.

Verified unused

axum, auto_impl, rand and hex are declared in [workspace.dependencies] and used by zero crates.

axum is a reservation for the health endpoint and should stay if #147 is imminent; the other three are dead.

The hoist that does not hold

wit-bindgen is hoisted with a comment claiming a single bump moves every guest module in lock-step.
Every guest module re-declares the literal version instead, because modules/ deliberately does not inherit [workspace.dependencies].
Either the comment is wrong or the hoist is pointless; decide which and fix that one.

Worth considering while there

auto_impl is declared and unused despite Arc<dyn Extension<T>>, Arc<dyn HostWallClock>, RunLogStore, StateStore and LogSink all being Arc-held.
reth #[auto_impl]s virtually every provider and host trait, which is what makes Arc<T> and &T interchangeable at those seams.
So the choice is to use it or drop it, not to leave it declared.

Done when

No declared workspace dependency is unused, and the wit-bindgen comment matches reality.