Add trust quorum proxy endpoints and use serde_with for hex encoding

Add three new proxy endpoints to the sled-agent API that allow forwarding
trust quorum operations to other nodes:

- POST `/trust-quorum/proxy/commit`
- POST `/trust-quorum/proxy/prepare-and-commit`
- POST `/trust-quorum/proxy/status`

Also refactors the trust quorum types to use `serde_with` with `Hex` encoding
for cleaner serialization of digests and encrypted rack secrets, replacing
manual hex string parsing with automatic encoding/decoding.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: plaidfinch

Cargo.lock

@@ -993,5 +993,47 @@ mod api_impl {
         > {
             unimplemented!()
         }
+
+        async fn trust_quorum_proxy_commit(
+            _request_context: RequestContext<Self::Context>,
+            _body: TypedBody<
+                sled_agent_types::trust_quorum::TrustQuorumProxyCommitRequest,
+            >,
+        ) -> Result<
+            HttpResponseOk<
+                sled_agent_types::trust_quorum::TrustQuorumCommitResponse,
+            >,
+            HttpError,
+        > {
+            unimplemented!()
+        }
+
+        async fn trust_quorum_proxy_prepare_and_commit(
+            _request_context: RequestContext<Self::Context>,
+            _body: TypedBody<
+                sled_agent_types::trust_quorum::TrustQuorumProxyPrepareAndCommitRequest,
+            >,
+        ) -> Result<
+            HttpResponseOk<
+                sled_agent_types::trust_quorum::TrustQuorumCommitResponse,
+            >,
+            HttpError,
+        > {
+            unimplemented!()
+        }
+
+        async fn trust_quorum_proxy_status(
+            _request_context: RequestContext<Self::Context>,
+            _body: TypedBody<
+                sled_agent_types::trust_quorum::TrustQuorumProxyStatusRequest,
+            >,
+        ) -> Result<
+            HttpResponseOk<
+                sled_agent_types::trust_quorum::TrustQuorumNodeStatus,
+            >,
+            HttpError,
+        > {
+            unimplemented!()
+        }
     }
 }