Fix Metadata's description for prettier printing

Sources/GRPCCore/Metadata.swift

@@ -494,15 +494,23 @@ extension Metadata.Value: ExpressibleByArrayLiteral {
 
 extension Metadata: CustomStringConvertible {
   public var description: String {
-    String(describing: self.map({ ($0.key, $0.value) }))
+    var description = "["
+    description = self.dropLast().reduce(into: description) { partialResult, nextPair in
+      partialResult += "\"\(nextPair.key)\": \(nextPair.value), "
+    }
+    if let lastElement = self.last {
+      description += "\"\(lastElement.key)\": \(lastElement.value)"
+    }
+    description += "]"
+    return description
   }
 }
 
 extension Metadata.Value: CustomStringConvertible {
   public var description: String {
     switch self {
     case .string(let stringValue):
-      return String(describing: stringValue)
+      return "\"\(stringValue)\""
     case .binary(let binaryValue):
       return String(describing: binaryValue)
     }

Tests/GRPCCoreTests/MetadataTests.swift

@@ -314,4 +314,17 @@ struct MetadataTests {
       )
     }
   }
+
+  @Suite("Description")
+  struct Description {
+    @Test("Metadata")
+    func describeMetadata() async throws {
+      let metadata: Metadata = [
+        "key1": "value1",
+        "key2": "value2",
+        "key-bin": .binary([1, 2, 3]),
+      ]
+      #expect("\(metadata)" == #"["key1": "value1", "key2": "value2", "key-bin": [1, 2, 3]]"#)
+    }
+  }
 }