Test failures on Python 3.12

### What happened?

When running `pytest` on Python 3.12 a bunch of tests fail with
```
RecursionError: maximum recursion depth exceeded
```
which seems to stem from
```
AttributeError("'bls12_381_FQ12' object has no attribute 'coeffs'") raised in repr()
```

### Code that produced the error

_No response_

### Full error output

_No response_

### Fill this section in if you know how this could or should be fixed

_No response_

### py-ecc Version

7.0.0

### Python Version

3.12.2

### Operating System

Linux

### Output from `pip freeze`

_No response_

Start by running pytest on Python 3.12.2 and capture the full traceback around bls12_381_FQ12.__repr__ and the missing coeffs attribute. Trace the recursion to its originating code and tests; done means the reported Python 3.12 failures no longer occur and the test suite passes.

Written by the indexing model from the issue text.