The Unique constraint cannot handle non-default index

[csala]

Environment Details

• SDV version: v0.12.0

Error Description

The internal implementation of the Unique constraint relies on the input data index.
Because of this, errors such as #616 and #610 happen, but other weird behaviors can be observed, such as the constraint consider that valid data is invalid:

In [30]: data = pd.DataFrame({'unique': [1, 2, 3]}, index=[0, 0, 0])

In [31]: unique.is_valid(data)
Out[31]: 
0     True
1    False
2    False
dtype: bool

Or producing inconsistent results:

In [38]: data = pd.DataFrame({'unique': [1, 2, 1]}, index=[0, 2, 1])

In [39]: unique.is_valid(data)
Out[39]: 
0     True
1    False
2     True
dtype: bool

We should review its implementation to prevent all these scenarios.