Create a function to convert regular text into leet (or hacker) speak by substituting specific letters with numbers.
The task involves working with a unique form of communication, "Leet speak" ("1337" or "hacker-speak"), that replaces English letters with numbers or symbols with a slight resemblance. You are required to create a function that converts standard text into leet speak. ### Specifications: Your function, named `to_leet_speak(txt: str) -> str`, should take in a regular text, `txt`, as an argument and replace 'a', 'e', 'i', 'o', and 's' with '4', '3', '1', '0', and '5' respectively. The input will only contain lowercase letters, spaces, and punctuation marks. The output should also be a string, represented in leet speak. ### Examples: ```python # Example 1: # In the sentence "python is cool", 'o' and 's' are replaced with '0' and '5' respectively. to_leet_speak("python is cool") # Returns: "pyth0n 15 c00l" # Example 2: # In the sentence "programming is fun", 'o', 'a', 'i', and 's' are replaced with '0', '4', '1', and '5' respectively. to_leet_speak("programming is fun") # Returns: "pr0gr4mm1ng 15 fun" # Example 3: # In the sentence "become a coder", 'o', 'e', and 'a' are replaced with '0', '3', and '4' respectively. to_leet_speak("become a coder") # Returns: "b3c0m3 4 c0d3r" ```