chore(deps): remove unused dependency declarations

[shikokuchuo]

Removes 59 unused dependency declarations across 27 crates — manifest hygiene, no source changes.

What we used

cargo-machete (--with-metadata) to find unused deps, then Claude verified every hit "by hand" before removing it.

Intentionally risk-averse

We removed only declarations with zero usage and left anything that looks unused but isn't. Kept on purpose:

• openssl-sys (quarto) — link-only, behind the vendored-openssl feature
• quarto-error-message-macros (quarto-parse-errors) — proc-macro; derive name ≠ crate name
• tokio (quarto-lsp-core) — macro-based usage
• sha2 (quarto-sass) — used in build.rs (machete doesn't scan build scripts)
• cc + the wasm/fuzz/patch-crate deps — left untouched

Impact

Only pretty_assertions (+ diff) drops from the build graph entirely; the rest were redundant declarations of crates still used elsewhere.

How we tested

Full cargo xtask verify — all 14 steps green, covering cargo build --workspace, cargo nextest run --workspace, the WASM rebuild, and the hub-client build/tests. The all-targets build is itself the proof: any test relying on a removed dev-dep would have failed to compile.

Strand: bd-e3lv7eg3.

[cscheid]

I think I'm missing something here, because a lot of the lines being removed reference crates we do need (ariadne, for example). Can you clarify what this is trying to do?

[shikokuchuo]

I had Claude just double-check on Ariadne as you mentioned it.

• pampa declared ariadne = "0.6" but has no use for ariadne anywhere in its source. The only real consumer is quarto-error-reporting;
• pampa gets ariadne formatting transitively through it. So pampa's declaration was redundant — ariadne stays in Cargo.lock and pampa still builds.

I was just trying to see how much we could clean up 'for free' - and it seems not much: the only 2 crates removed are diff and pretty_assertions as nothing used them at all.

[cscheid]

Ok, got it. I'm fine with merging this, I just wanted to know the context (we also have a lockfile conflict somehow).

[shikokuchuo]

I just wanted to share the result really as I'd attempted it... I've re-based so should be ok to merge.

Also fine not to merge, and leave this all for later...