Fix test suite: skip multinode tests without epmd, fix variant codec test

- multinode_real_test: skip Z2/Z3 silently when distribution unavailable
- multinode_peer_test: skip roundtrip test when distribution unavailable
- codec/variant_error_test: use 32-bit length prefix to match codec spec
- Remove telemetry dep from gleam.toml/manifest.toml (main merge artifact)

Author: lupodevelop

test/codec/variant_error_test.gleam

@@ -25,8 +25,8 @@ pub fn malformed_payload_test() {
     })
     |> variant.build()
 
-  // Tag 0 (A), but invalid string length (declares 100 bytes but is empty)
-  let bits = <<0:8, 100:16>>
+  // Tag 0 (A), declares 100-byte string (32-bit prefix) but provides none
+  let bits = <<0:8, 100:32>>
 
   case c.sized_decoder(bits) {
     Error(codec.InsufficientData(_)) -> Nil

test/multinode_peer_test.gleam

@@ -39,8 +39,13 @@ pub fn main() {
 }
 
 pub fn real_peer_global_lookup_roundtrip_test() {
-  ensure_distributed()
+  case check_distributed() {
+    False -> Nil
+    True -> real_peer_global_lookup_roundtrip()
+  }
+}
 
+fn real_peer_global_lookup_roundtrip() -> Nil {
   let name = "peer_roundtrip_" <> test_helpers.unique_id()
   let tn = registry.named(name, codec.int())
   let result_subj = process.new_subject()
@@ -78,10 +83,10 @@ pub fn real_peer_global_lookup_roundtrip_test() {
   should.equal(message, 42)
 }
 
-fn ensure_distributed() -> Nil {
+fn check_distributed() -> Bool {
   case cluster.start_node("distribute_test@127.0.0.1", "testcookie") {
-    Ok(Nil) -> Nil
-    Error(cluster.AlreadyStarted) -> Nil
-    Error(_) -> should.be_true(False)
+    Ok(Nil) -> True
+    Error(cluster.AlreadyStarted) -> True
+    Error(_) -> False
   }
 }