Use st_birthtimespec instead of st_ctim.tv_sec on Darwin

st_ctim records the last time the inode changed. Closest thing on linux, but st_birthtimespec is what we actually want here.

Author: AZero13

Sources/FoundationEssentials/FileManager/FileManager+Files.swift

@@ -155,7 +155,7 @@ extension stat {
 
     var creationDate: Date {
         #if canImport(Darwin)
-        Date(seconds: TimeInterval(st_ctimespec.tv_sec), nanoSeconds: TimeInterval(st_ctimespec.tv_nsec))
+        Date(seconds: TimeInterval(st_birthtimespec.tv_sec), nanoSeconds: TimeInterval(st_birthtimespec.tv_nsec))
         #else
         Date(seconds: TimeInterval(st_ctim.tv_sec), nanoSeconds: TimeInterval(st_ctim.tv_nsec))
         #endif

Tests/FoundationEssentialsTests/FileManager/FileManagerTests.swift

@@ -1093,6 +1093,24 @@ private struct FileManagerTests {
     }
     #endif
 
+    @Test(.enabled(if: isDarwin, "Birth time is only exposed on Darwin"))
+    func creationDateUsesBirthTime() async throws {
+        try await FilePlayground {
+            File("file")
+        }.test { fileManager in
+            let attrs1 = try fileManager.attributesOfItem(atPath: "file")
+            let creation1 = try #require(attrs1[.creationDate] as? Date)
+
+            // Mutate metadata to advance ctime without touching birth time
+            try fileManager.setAttributes([.posixPermissions: 0o600], ofItemAtPath: "file")
+
+            let attrs2 = try fileManager.attributesOfItem(atPath: "file")
+            let creation2 = try #require(attrs2[.creationDate] as? Date)
+
+            #expect(creation1 == creation2, "Creation date should remain stable when metadata changes (uses birth time, not ctime)")
+        }
+    }
+
     #if canImport(Darwin)
     @Test func SearchPathsWithoutExpandingTilde() async throws {
         for path in _DarwinSearchPaths(for: .libraryDirectory, in: .userDomainMask, expandTilde: false) {