fix: aead unit tests no longer deadlock

* fix: add back unit tests and configure rayon threadpool

* Use env var to set rayon threads.

* Remove `rayon` dev dependency.

.github/workflows/ci.yml

@@ -13,6 +13,12 @@ on:
 env:
   CARGO_TERM_COLOR: always
   CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
+  # We need a higher number of parallel rayon tasks than the default (which is 4)
+  # in order to prevent a deadlock, c.f.
+  #   - https://github.com/tlsnotary/tlsn/issues/548
+  #   - https://github.com/privacy-scaling-explorations/mpz/issues/178
+  # 32 seems to be big enough for the foreseeable future
+  RAYON_NUM_THREADS: 32
 
 jobs:
   fmt:

crates/components/aead/src/aes_gcm/error.rs

@@ -19,10 +19,10 @@ impl AesGcmError {
         }
     }
 
-    //    #[cfg(test)]
-    //    pub(crate) fn kind(&self) -> ErrorKind {
-    //        self.kind
-    //    }
+    #[cfg(test)]
+    pub(crate) fn kind(&self) -> ErrorKind {
+        self.kind
+    }
 
     pub(crate) fn invalid_tag() -> Self {
         Self {