chore(deps): bump hyperlane and hyperlane-core to 21.12.0

[vshengbro]

Summary

Bump hyperlane and hyperlane-core requirements to 21.12.0 (from 21.3.6 / 21.7.6).

hyperlane-core 21.12.0 changes Server::route to pub fn route<S>(&mut self, path: impl AsRef<str>) (hyperlane-dev/hyperlane#43). This repository registers all 131 routes through the #[route] attribute macro, which uses inventory::submit! + HookType::Route and never calls Server::route — so no route call sites change here (grep -rn 'route::<' returns 0).

One adaptation is required for a different change shipping in the same release: 21.12.0 reduces http-constant's DATE header-name constant to pub(crate) (hyperlane §18 const-visibility sweep, commit 684f3c0). The response header middleware used that constant, so it now carries its own local copy:

• application/middleware/request/const.rs (new) — pub(crate) const DATE: &str = "date";
• application/middleware/request/mod.rs — wire mod r#const; + pub(crate) use r#const::*;

Cargo.lock intentionally still pins 21.11.0: crates.io only serves 21.12.0 after hyperlane-dev/hyperlane#43 merges and the publish workflow runs. Refresh with cargo update -p hyperlane afterwards.

Verification

Verified locally with a temporary [patch.crates-io] pointing at the hyperlane 21.12.0 working tree (patch section removed before commit):

• cargo build --workspace — clean (21.12.0 path-patched)
• cargo clippy --workspace --all-targets — 0 code warnings/errors
• cargo test --workspace --all-features — all suites pass (0 tests exist in this workspace)
• cargo fmt --all + --check — 0 diff, idempotent
• staged_file_gate.py (pre-commit hook) — 0 new violations
• No route::<T, P> patterns exist anywhere in the codebase

Notes

• Blocked on feat(server): infer route path type via impl AsRef<str> parameter hyperlane#43: CI here cannot resolve hyperlane = "21.12.0" until that PR merges and the publish job uploads 21.12.0 to crates.io. Merge this only after the lockfile refresh succeeds.
• Playground branch gets the same treatment in a separate PR.