Need a Python function that takes a string and an integer k as inputs and returns a list of unique substrings containing only consonants (non-vowel characters) with a maximum length of k within the given string. Only through recursion
For instance, given the string "abcde" and k = 2, the function should return 5 substrings with only consonants and a maximum length of 2: "b", "c", "d", "bc", "cd".Should handle edge cases such as empty strings, strings with no consonants, different cases (lowercase/uppercase), and efficiently considers the constraint of the maximum length of consonant substrings.