Reduce the number of iterations to 100,000

Also factor out the number of iterations so future
tinkerers have a way to experiment.

Author: tbkka

Tests/SwiftProtobufTests/Test_AsyncMessageSequence.swift

@@ -202,9 +202,12 @@ final class Test_AsyncMessageSequence: XCTestCase {
 
   // Slow test case found by oss-fuzz: 1 million zero-sized messages
   // A similar test with BinaryDelimited is about 4x faster, showing
-  // that we have some room for improvement here:
+  // that we have some room for improvement here.
+  // (Note this currently only tests 100,000 zero-sized messages,
+  // but the constant below is easy to edit if you want to experiment.)
   func testLargeExample() async throws {
-    let bytes = [UInt8](repeating: 0, count: 1000000)
+    let messageCount = 100_000
+    let bytes = [UInt8](repeating: 0, count: messageCount)
     let byteStream = asyncByteStream(bytes: bytes)
     let decodedStream = byteStream.binaryProtobufDelimitedMessages(
                     of: SwiftProtoTesting_TestAllTypes.self,
@@ -214,7 +217,7 @@ final class Test_AsyncMessageSequence: XCTestCase {
       XCTAssertEqual(message, SwiftProtoTesting_TestAllTypes())
       count += 1
     }
-    XCTAssertEqual(count, 1000000)
+    XCTAssertEqual(count, messageCount)
   }
 
   fileprivate func asyncByteStream(bytes: [UInt8]) -> AsyncStream<UInt8> {

Tests/SwiftProtobufTests/Test_BinaryDelimited.swift

@@ -148,10 +148,11 @@ final class Test_BinaryDelimited: XCTestCase {
   // oss-fuzz found this case that runs slowly for AsyncMessageSequence
   // Copied here as well for comparison.
   func testLargeExample() throws {
-    let bytes = [UInt8](repeating: 0, count: 1000000)
+    let messageCount = 100_000
+    let bytes = [UInt8](repeating: 0, count: messageCount)
     let istream = openInputStream(bytes)
 
-    for _ in 0..<1000000 {
+    for _ in 0..<messageCount {
       let msg = try BinaryDelimited.parse(
 	messageType: SwiftProtoTesting_TestAllTypes.self,
 	from: istream)