feat(server): infer route path type via impl AsRef<str> parameter

[vshengbro]

Summary

Server::route drops its explicit P generic and takes path: impl AsRef<str> instead:

// before
pub fn route<S, P>(&mut self, path: P) -> &mut Self
where
    S: ServerHook,
    P: AsRef<str>;

// after
pub fn route<S>(&mut self, path: impl AsRef<str>) -> &mut Self
where
    S: ServerHook;

Callers now write server.route::<TestRoute>("/") without naming the path type. The impl AsRef<str> parameter is the inference shim exempted by rust-standards §9.2a, so &str, String and &String call sites keep compiling and method chaining still works.

Breaking change: turbofish call sites that named the path type explicitly (route::<T, &str>(path)) no longer compile — the method now takes exactly one generic argument (E0107). All 42 in-tree call sites are updated in this commit:

• core/tests/route/fn.rs — 22 call sites + new route_path_type_inference test
• core/tests/server/fn.rs — 18 call sites
• plugin/websocket/tests/websocket/fn.rs — 2 call sites

Workspace version bumped 21.11.0 → 21.12.0 ([workspace.package] only; [workspace.dependencies] path versions synced via crate sync). The #[route] proc-macro registers routes via inventory::submit! + HookType::Route and does not call Server::route, so hyperlane-macros is unaffected. hyperlane-cli and the root hyperlane shim never wrap route.

Verification

• cargo build --workspace — clean
• cargo clippy --workspace --all-targets — 0 warnings, 0 errors
• cargo test --workspace --all-features — all pass, 694 assertions total; route::r#fn::route_path_type_inference ... ok covers &str, String, &String and chained registration
• cargo fmt --all + cargo fmt --all -- --check — 0 diff, idempotent
• rust-standards audit: 50/51 PASS, identical to the origin/master baseline (the single FAIL is check 49 §18 const-visibility, 2114 pre-existing hits in 12 files on both trees — zero new violations introduced by this change)
• staged_file_gate.py (pre-commit hook) — 0 new violations, commit allowed
• Backward-compat probe (not committed): route::<TestRoute, &str>("/") now fails with E0107 as expected — this is the breaking half of the change, which is why the call-site updates and the minor bump ship together

Notes

• Repo rebased onto eea52fa (PR chore: centralize test std imports into tests mod.rs (§6.4, check 26) #41) before commit; no overlap with that PR's type/tests files.
• Follow-up after merge: hyperlane-quick-start (master + playground) bumps its hyperlane / hyperlane-core requirement to 21.12.0 once crates.io serves it.
• The §18 check-49 debt (2114 pub const hits) is pre-existing on master and out of scope here; it needs its own sweep PR.