Fix error when using multiline lambdas in until method

[ppopov212]

I know multi-line lambdas in Python sounds strange, but hear me out. In a project of mine, I use Black for code formatting, and Black sometimes can format l long lambdas like this

wait().at_most(5).until_asserted(
        lambda: (
            super_long_assert_assert_function(
                param1,
                param2,
                param3,
                param4,
            )
        )
    )

So in this case busypie fails with the following message

AttributeError: 'NoneType' object has no attribute 'group'

After some digging, I found that busypie inspects the lambda function and runs a regex on the source. In this case, the regex is failing to match. I'm talking about this function in func.py file

def _content_of(lambda_func: Callable) -> str:
    source_line = inspect.getsource(lambda_func)
    r = re.search(r'lambda[^:]*:\s*(.+)\s*\)', source_line) # <- this regex fails to math the source code of the lambda
    return r.group(1)   

My naive solution for a fix is to replace one or more whitespace characters with a single whitespace character. This removes the new lines and the regex is matching now. I've run the tests and they all pass

[rockem]

@ppopov212 Thanks for the PR, can you also add a test for this new functionality?

[ppopov212]

Sure, I'll add one

[ppopov212]

@rockem I've added a test, I hope it's ok 🤞

[ppopov212]

@rockem I've made changes, you can check them 🙏

[rockem]

Very nice!

[rockem]

The problem with this solution is that it will work on strings and comments
So in order to resolve it we need something more sophisticated.
So, I think we can live with it in the description for now, and keep this PR simple
wdyt?

[rockem]

?