`and`ed expressions evaluate different objects unless parenthesized

### Bug Description

According to [the documentation](https://checkbox.readthedocs.io/en/latest/reference/units/resource.html#exactly-one-resource-bound-to-a-variable-at-once):
> It’s not possible to refer to two different resources, from the same resource group, in one resource expression.

Consider this test:

```python
def test_evaluate_same_object(self):
resource_map = {
'a': [Resource({'foo': 1, 'baz': 'b'}), Resource({'foo': 2, 'baz': 'a'})],
}
expr = ResourceExpression("a.foo == 1 and a.baz != 'b'")
self.assertFalse(expr.evaluate(
resource_map['a'],
resource_map=resource_map
))
```

And it failing:
```
FAIL: test_evaluate_same_object (plainbox.impl.test_resource.ResourceExpressionTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/michal/dev/canonical/checkbox/checkbox-ng/plainbox/impl/test_resource.py", line 426, in test_evaluate_same_object
self.assertFalse(expr.evaluate(
AssertionError: True is not false
```

There is not a single resource whose `foo` is 1, and `baz` is not `b`. But the expression succeeds. Wrapping the first expression in parentheses makes it work as intended.

### To Reproduce

Run the above test.

### Environment

N/A

### Relevant log output

_No response_

### Additional context

_No response_

Start with plainbox/impl/test_resource.py and ResourceExpressionTests.test_evaluate_same_object, using the reproducer from the issue. Then trace ResourceExpression evaluation to understand why the two sides of the `and` use different resources. Done means the unparenthesized expression evaluates false and the regression test passes.

Written by the indexing model from the issue text.