Testing improvements

# 💬 RFC

Goals:
- [x] Easier to write unit tests (no need to understand `responses` API) (#424)
- [ ] End-to-end (E2E) tests for workflows
- Continuous mastering
- Continuous categorization
- Setup mastering project
- [ ] Track Tamr versions: "which was the most recent version of Tamr this ran successfully on?"
- [ ] (Ideal) property-based tests

## 🔦 Context

## 💻 Examples

```python
import pytest

import tamr_client as tc
from tests.utils import fake_tamr

@fake_tamr
@given(s=session, i=instance)
def test_from_resource_id_mastering(s: Session, i: Instance):
p = tc.project.from_resource_id(s, instance, "1")

assert isinstance(p, tc.MasteringProject)
assert p.name == "proj"
assert p.description == "Mastering Project"
```