fix(test): delete setTimeout.clock property when disabling fake timers (#26285)

## Summary

- Fixes the `setTimeout.clock` property not being properly deleted after
`jest.useRealTimers()` is called
- Previously, the property was set to `false` instead of deleted,
causing `hasOwnProperty` checks to return `true`
- This broke React Testing Library and other libraries that check for
fake timers using `Object.prototype.hasOwnProperty.call(setTimeout,
'clock')`

## Changes

- Added `JSValue.deleteProperty()` binding in Zig to call JSC's
`deleteProperty()` method
- Updated `setFakeTimerMarker()` in `FakeTimers.zig` to delete the
`clock` property when disabling fake timers
- Updated existing test in `test/regression/issue/25869.test.ts` to
verify correct behavior
- Added new regression test in `test/regression/issue/26284.test.ts`

## Test plan

- [x] Verified new test fails with system bun (before fix)
- [x] Verified new test passes with debug build (after fix)
- [x] Verified existing fake timer tests still pass
- [x] Verified test for issue #25869 passes with fix

Fixes #26284

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

test/regression/issue/25869.test.ts

@@ -32,13 +32,13 @@ test("setTimeout.clock is set after useFakeTimers", () => {
   }
 });
 
-test("setTimeout.clock is set to false after useRealTimers", () => {
+test("setTimeout.clock is deleted after useRealTimers", () => {
   jest.useFakeTimers();
   jest.useRealTimers();
-  // Note: The clock property remains on setTimeout but is set to false.
-  // This differs from Jest/Sinon which removes the property entirely.
-  // The value being false is sufficient for most use cases.
-  expect((globalThis.setTimeout as any).clock).toBe(false);
+  // The clock property should be deleted when disabling fake timers.
+  // This matches Jest/Sinon behavior and ensures hasOwnProperty returns false.
+  expect(Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")).toBe(false);
+  expect((globalThis.setTimeout as any).clock).toBe(undefined);
 });
 
 test("advanceTimersByTime(0) fires setTimeout(fn, 0) timers", async () => {

test/regression/issue/26284.test.ts

@@ -0,0 +1,67 @@
+// https://github.com/oven-sh/bun/issues/26284
+// After useRealTimers(), hasOwnProperty('clock') should return false
+import { afterEach, expect, jest, test } from "bun:test";
+
+// Simulates testing-library/react's jestFakeTimersAreEnabled() function
+function jestFakeTimersAreEnabled(): boolean {
+  // @ts-expect-error - checking for Jest fake timers markers
+  if (typeof jest !== "undefined" && jest !== null) {
+    return (
+      // @ts-expect-error - checking for mock function marker
+      (globalThis.setTimeout as any)._isMockFunction === true ||
+      Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")
+    );
+  }
+  return false;
+}
+
+// Ensure fake timers are always cleaned up after each test
+afterEach(() => {
+  jest.useRealTimers();
+});
+
+test("hasOwnProperty('clock') returns false before useFakeTimers", () => {
+  expect(Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")).toBe(false);
+  expect(jestFakeTimersAreEnabled()).toBe(false);
+});
+
+test("hasOwnProperty('clock') returns true after useFakeTimers", () => {
+  jest.useFakeTimers();
+  expect(Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")).toBe(true);
+  expect((globalThis.setTimeout as any).clock).toBe(true);
+  expect(jestFakeTimersAreEnabled()).toBe(true);
+});
+
+test("hasOwnProperty('clock') returns false after useRealTimers", () => {
+  // First enable fake timers
+  jest.useFakeTimers();
+  expect(Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")).toBe(true);
+
+  // Then disable them
+  jest.useRealTimers();
+
+  // The clock property should be deleted, not just set to false
+  expect(Object.prototype.hasOwnProperty.call(globalThis.setTimeout, "clock")).toBe(false);
+  expect((globalThis.setTimeout as any).clock).toBe(undefined);
+  expect(jestFakeTimersAreEnabled()).toBe(false);
+});
+
+test("multiple useFakeTimers/useRealTimers cycles work correctly", () => {
+  // Cycle 1
+  jest.useFakeTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(true);
+  jest.useRealTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(false);
+
+  // Cycle 2
+  jest.useFakeTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(true);
+  jest.useRealTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(false);
+
+  // Cycle 3
+  jest.useFakeTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(true);
+  jest.useRealTimers();
+  expect(jestFakeTimersAreEnabled()).toBe(false);
+});