fix(concurrency): make DateSection nonisolated to silence #expect warnings

5 个 Swift Testing macro 展开的 warning:DateSection 的 Equatable 协议被默认
推到 MainActor,但 #expect 在 nonisolated context 比较 — Swift 6 严格模式会报错。

康康/Features/Timeline/DateSection.swift

@@ -1,6 +1,6 @@
 import Foundation
 
-enum DateSection: Hashable {
+nonisolated enum DateSection: Hashable {
     case today
     case yesterday
     case thisWeek