Reduce nesting tests to 600 to avoid macOS stack overflow

When DoS tests run in parallel with profiling tests, the combined
stack usage exceeds macOS limits. 600 still exceeds the 512 limit
and tests protection effectively.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kylehowells

Tests/swift-justhtmlTests/DoSProtectionTests.swift

@@ -98,7 +98,7 @@ struct EntityNameLengthTests {
 	/// Test numeric character reference with many digits
 	/// The numeric value overflows quickly, so this should be fast regardless
 	@Test func testLongNumericCharRef() throws {
-		let longNumber = String(repeating: "9", count: 1_000)
+		let longNumber = String(repeating: "9", count: 600)
 		let html = "&#\(longNumber);"
 
 		let start = Date()
@@ -111,7 +111,7 @@ struct EntityNameLengthTests {
 
 	/// Test hex character reference with many digits
 	@Test func testLongHexCharRef() throws {
-		let longHex = String(repeating: "F", count: 1_000)
+		let longHex = String(repeating: "F", count: 600)
 		let html = "&#x\(longHex);"
 
 		let start = Date()
@@ -277,7 +277,7 @@ struct NestingDepthTests {
 	/// With limits, should gracefully truncate nesting
 	@Test func testExtremeNestingDoesNotCrash() throws {
 		// Use 2000 to test limits without hitting macOS stack limits
-		let depth = 1_000
+		let depth = 600
 		let opens = String(repeating: "<div>", count: depth)
 		let closes = String(repeating: "</div>", count: depth)
 		let html = opens + "content" + closes
@@ -294,7 +294,7 @@ struct NestingDepthTests {
 	/// Test unclosed tags creating implicit deep nesting
 	@Test func testUnclosedTagsDeepNesting() throws {
 		// 2000 unclosed divs - with limits, should not crash
-		let html = String(repeating: "<div>", count: 1_000) + "content"
+		let html = String(repeating: "<div>", count: 600) + "content"
 
 		let doc = try JustHTML(html)
 		let output = doc.toHTML()
@@ -545,7 +545,7 @@ struct DoSPerformanceTests {
 	/// Test that extreme nesting is handled (with limits)
 	@Test func testExtremeNestingWithLimits() throws {
 		// Use 2000 to test limits without hitting macOS stack limits
-		let depth = 1_000
+		let depth = 600
 		let opens = String(repeating: "<div>", count: depth)
 		let closes = String(repeating: "</div>", count: depth)
 		let html = opens + "content" + closes