MockRequest does not work for response data of type Buffer

[katrotz]

The change introduced in this PR#294 that clones the fixtures breaks the tests where the mocks are Buffers.
Same happens when the response is a typed array (eg. Uint8Array)

Expected:
When the mockRequest body is not a plain object, do not clone it, or clone it using specialised methods (eg. for Buffers Buffer.from, for Uint8Array Uint8Array.from, etc.)

Actual:
The buffer mock response is cloned into a plain object

[klippx]

Related: #286

[klippx]

The fix has now been relased in 2.38.1