Add tests for ordinary-index search

[jeltsch]

We shall add property-based tests for the search function of the ordinary index.

Furthermore, we shall add property-based tests for the binarySearchL function for immutable vectors, which is used by search, in case we haven’t ended up implementing that function by reusing binarySearchL from vector-algorithms.

[jeltsch]

Property-based tests for the search function are now available as part of #362.

Property-based tests for the binarySearchL function aren’t necessary, since we have ended up implementing this function by reusing binarySearchL from vector-algorithms (see #256).