SAConnection twophase methods are broken

### Describe the bug

1. begin_twophase() is not a context manager
2. recover_twophase() is broken
3. rollback_prepared() is broken

### To Reproduce

just use these methods)

### Expected behavior

1. begin_twophase() behaves as a context manager, using commit_prepared() at the end OR docs changed to reflect current implementation
2. does not crash on accessing ResultProxy
3. does not crash on string formatting

### Logs/tracebacks

#### 1. begin_context() is not a context

According to docs: https://aiopg.readthedocs.io/en/stable/sa.html#aiopg.sa.SAConnection.begin_twophase

> coroutine async-with begin_twophase(xid=None)

but in reality:

```python-traceback
async with conn.begin_twophase() as transaction:
AttributeError: __aenter__
```

#### 2. recover_twophase() is broken

result is not awaited:

```python-traceback
File "/Users/ovmikhaylov/work/aiopg/aiopg/sa/connection.py", line 363, in recover_twophase
return [row[0] for row in result]
TypeError: 'ResultProxy' object is not iterable
```

#### 3. rollback_prepared() is broken

Due to error in f-string:

```python-traceback
File "/Users/ovmikhaylov/work/aiopg/aiopg/sa/connection.py", line 368, in rollback_prepared
await self.execute(f"ROLLBACK PREPARED {xid:!r}")
ValueError: Invalid format specifier
```

### Python Version

```console
3.10
```

### aiopg Version

```console
1.3.3
```

### OS

Darwin gmbp.local 20.6.0 Darwin Kernel Version 20.6.0: Tue Oct 12 18:33:42 PDT 2021; root:xnu-7195.141.8~1/RELEASE_X86_64 x86_64

### Additional context

_No response_

### Code of Conduct

- [X] I agree to follow the aio-libs Code of Conduct