Replace Prophecy with Native PHPUnit Mocks

### Feature Request

|    Q        |   A
|------------ | ------
| New Feature | yes
| RFC         | no
| BC Break    | no

#### Summary

All of the tests need to be altered to use native PHPUnit Mocks instead of Prophecy. Prophecy needs removing from dependencies. A huge chunk of the Psalm baseline is due to prophecy usage here.
