feat(sns): neuron SetFollowing command is validated in isolation (#4543)

This PR adds validation for the recently added neuron `SetFollowing`
command (which is still disabled). The validation is based on global
topic following invariants, but does not yet take into potential account
existing topic-based following that a neuron might have; that will be
added in a follow-up PR.

| [Next PR](#4563) >

Author: aterga

Cargo.lock

@@ -66,6 +66,7 @@ DEPENDENCIES = [
     "@crate_index//:serde_bytes",
     "@crate_index//:serde_json",
     "@crate_index//:strum",
+    "@crate_index//:thiserror",
 ]
 
 MACRO_DEPENDENCIES = [

rs/sns/governance/BUILD.bazel

@@ -84,6 +84,7 @@ serde_json = { workspace = true }
 strum = { workspace = true }
 strum_macros = { workspace = true }
 canbench-rs = { version = "0.1.7", optional = true }
+thiserror = { workspace = true }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
 ic-types = { path = "../../types/types" }

rs/sns/governance/Cargo.toml

@@ -56,7 +56,12 @@ pub fn generate_prost_files(proto: ProtoPaths<'_>, out: &Path) {
     };
     apply_attribute(
         "#[derive(strum_macros::EnumIter)]",
-        vec!["Governance.Mode", "NeuronPermissionType", "Proposal.action"],
+        vec![
+            "Governance.Mode",
+            "NeuronPermissionType",
+            "Proposal.action",
+            "Topic",
+        ],
     );
     apply_attribute(
         "#[derive(serde::Serialize)]",