Tests are 2x slower when upgrading from vitest 3 to vitest 4

[guillaume-docquier-vention]

I've upgraded vitest and I am seeing slow test times now. Used to be 300ms, now is 600ms.
I haven't seen anyone talk about that in the issues or discussions.

I've seen this in 2 of my repos where I tried.
It's company code, so I can't really share things, but here's the test output

Before

> @redacted/project@0.7.1 test
> vitest


 DEV  v3.0.5 /redacted/path/to/project

 ✓ src/Result.test.ts (10 tests) 6ms
 ✓ src/errors/FatalError.test.ts (9 tests) 7ms
 ✓ src/TypeGuard.test.ts (176 tests) 20ms
 ✓ src/Assert.test.ts (94 tests | 4 skipped) 19ms
 ✓ src/errors/AssertionError.test.ts (7 tests) 3ms
 ✓ src/utility-types.test.ts (3 tests) 1ms
 ✓ src/errors/NotImplementedError.test.ts (4 tests) 1ms
 ✓ src/throttleConcurrency.test.ts (4 tests) 14ms
 ✓ src/errors/Rethrow.test.ts (37 tests) 8ms
 ✓ src/getEnumKey.test.ts (5 tests) 1ms
 ✓ src/errors/isNodeJSError.test.ts (9 tests) 1ms
 ✓ src/errors/isError.test.ts (9 tests) 1ms
 ✓ src/asArray.test.ts (2 tests) 0ms

 Test Files  13 passed (13)
      Tests  365 passed | 4 skipped (369)
   Start at  13:32:53
   Duration  374ms (transform 216ms, setup 0ms, collect 319ms, tests 81ms, environment 1ms, prepare 214ms)

 PASS  Waiting for file changes...
       press h to show help, press q to quit

After

> @redacted/project@0.7.2 test
> vitest


 DEV  v4.0.15 /redacted/path/to/project

 ✓ src/errors/AssertionError.test.ts (7 tests) 14ms
 ✓ src/throttleConcurrency.test.ts (4 tests) 18ms
 ✓ src/errors/FatalError.test.ts (9 tests) 18ms
 ✓ src/errors/Rethrow.test.ts (37 tests) 19ms
 ✓ src/TypeGuard.test.ts (176 tests) 35ms
 ✓ src/Assert.test.ts (94 tests | 4 skipped) 27ms
 ✓ src/getEnumKey.test.ts (5 tests) 6ms
 ✓ src/asArray.test.ts (2 tests) 5ms
 ✓ src/errors/NotImplementedError.test.ts (4 tests) 7ms
 ✓ src/errors/isError.test.ts (9 tests) 5ms
 ✓ src/Result.test.ts (10 tests) 9ms
 ✓ src/errors/isNodeJSError.test.ts (9 tests) 8ms
 ✓ src/utility-types.test.ts (3 tests) 4ms

 Test Files  13 passed (13)
      Tests  365 passed | 4 skipped (369)
   Start at  13:30:14
   Duration  615ms (transform 322ms, setup 0ms, import 634ms, tests 175ms, environment 3ms)

 PASS  Waiting for file changes...
       press h to show help, press q to quit