More Strict Error Equality fails with mswjs HttpResponse.error()

Describe the bug

mswjs uses another way to add the cause of an error to the error itself, so the diff, based on keys
eq({...a}, {....b) ...
fails, but should not
currently we will remove the cause from the expected result manually to compare without it.

Reproduction

const NewError = new Error('hi');
const NewErrorWithCause = new Error('hi', { cause: 'x' });
const NewErrorWithAssignedCause = Object.assign(new Error('hi'), {
    cause: 'x',
});

// examples from https://vitest.dev/guide/migration.html#more-strict-error-equality
// same as
// expect(new Error('hi', { cause: 'x' })).toEqual(new Error('hi')); // ✅
expect(NewErrorWithCause).toEqual(NewError); // ✅
// same as 
// expect(new Error('hi')).toEqual(new Error('hi', { cause: 'x' })); // ❌
expect(NewError).toEqual(NewErrorWithCause); // ❌

// examples based on
// https://github.com/mswjs/interceptors/blob/7410d45a919bacadc2995d6173f3f7e7340f6e50/src/interceptors/fetch/utils/createNetworkError.ts
// https://github.com/mswjs/interceptors/blob/main/src/interceptors/fetch/utils/createNetworkError.ts
expect(NewErrorWithAssignedCause).toEqual(NewError); // should be ✅ -> but is ❌
expect(NewErrorWithAssignedCause).toEqual(NewErrorWithCause); // should be ✅ -> but is ❌

### System Info

```shell
System:
    OS: Windows 11 10.0.22631
    CPU: (16) x64 12th Gen Intel(R) Core(TM) i7-1260P
    Memory: 12.65 GB / 31.71 GB
Binaries:
    Node: 22.16.0
    npm: 10.9.2
Browsers:
    Edge: Chromium (132.0.2957.140)
    Internet Explorer: 11.0.22621.3527

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

Start by reproducing the examples in the issue around more-strict error equality, including errors created with Error.cause and errors whose cause is assigned afterward. Read the linked Vitest migration guidance and the referenced mswjs createNetworkError implementation to compare the error shapes. Done means the assigned-cause cases match the expected equality behavior without manual cause removal.