build(neuron): bump cudarc fork to 63327a2 (idempotent abort + Comm Send+Sync)

The fork's new commit makes `Comm: Send + Sync` (asserting NCCL's
thread-safety invariant upstream) and makes `Comm::abort` idempotent via
an `aborted` flag (so abort-then-Drop can't double-free) — strictly
better than the previous Drop-no-panic workaround, and the `abort()`
signature is unchanged so the watchdog call site is unaffected.

Because `Comm` is now `Send + Sync`, `Arc<Comm>` and the `SendComm` /
`NcclState` wrappers auto-derive `Send`/`Sync`, which conflicts (E0119)
with neuron's manual `unsafe impl`s. Remove the four now-redundant impls
— the safety assertion lives upstream in cudarc where it belongs. The
conflict is in cuda-gated code, so only the CUDA type-check catches it
(non-cuda build + clippy + tests stay green).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -69,4 +69,4 @@ cortex-gateway = { path = "crates/cortex-gateway" }
 # rebuild the comm). Pinned to a fork revision pending upstream review
 # (grenade/cudarc @ nccl-comm-abort).
 [patch.crates-io]
-cudarc = { git = "https://github.com/grenade/cudarc", rev = "dbc425aa865c178f38a3ec838f1f7a4da3146358" }
+cudarc = { git = "https://github.com/grenade/cudarc", rev = "63327a256059f8252641ae46c6bb9eefe707f382" }