Treat an unchanged map/list component as wire-compatible in diff (#119)

wireCompatibleScalars recursed into map and list types requiring both components
to be wire-compatible, but had no equality short-circuit. An unchanged component
that is not a member of a wire-compatible scalar group (e.g. a string map key)
returned false, dragging the whole verdict to incompatible. So a genuinely
wire-safe map value widening such as map<string,int32> -> map<string,int64>
was reported as an Error in Wire mode, failing CI on a safe change.

Short-circuit identical components to wire-compatible.

Author: ghostdogpr

tools/src/main/scala/proteus/ProtoDiff.scala

@@ -261,6 +261,7 @@ object ProtoDiff {
   )
 
   private def wireCompatibleScalars(oldType: Type, newType: Type): Boolean = (oldType, newType) match {
+    case (a, b) if a == b                             => true
     case (Type.ListType(x), Type.ListType(y))         => wireCompatibleScalars(x, y)
     case (Type.MapType(k1, v1), Type.MapType(k2, v2)) => wireCompatibleScalars(k1, k2) && wireCompatibleScalars(v1, v2)
     case (Type.String, Type.Bytes)                    => true

tools/src/test/scala/proteus/ProtoDiffSpec.scala

@@ -154,6 +154,20 @@ object ProtoDiffSpec extends ZIOSpecDefault {
         }
         assertTrue(results.forall(identity))
       },
+      test("wire-compatible map key/value widening is not breaking in Wire mode") {
+        val cases   = List(
+          ("map<string, int32>", "map<string, int64>"),
+          ("map<int32, string>", "map<int64, string>")
+        )
+        val results = cases.map { case (from, to) =>
+          val old     = parse(s"""syntax = "proto3"; message Foo { $from counts = 1; }""")
+          val nw      = parse(s"""syntax = "proto3"; message Foo { $to counts = 1; }""")
+          val changes = ProtoDiff.diff(old, nw)
+          changes.nonEmpty &&
+            changes.forall(c => ProtoDiff.severity(c, CompatMode.Wire) == Severity.Info)
+        }
+        assertTrue(results.forall(identity))
+      },
       test("field optionality changed") {
         val old = parse("""syntax = "proto3"; message Foo { string name = 1; }""")
         val nw  = parse("""syntax = "proto3"; message Foo { optional string name = 1; }""")