Text Normalizer

Implement a text normalizer that performs the following steps in order:

1. Convert to lowercase
2. Expand common contractions:
   • "don't" -> "do not"
   • "can't" -> "cannot"
   • "won't" -> "will not"
   • "i'm" -> "i am"
   • "it's" -> "it is"
   • "i've" -> "i have"
   • "they're" -> "they are"
   • "we're" -> "we are"
   • "you're" -> "you are"
   • "isn't" -> "is not"
   • "aren't" -> "are not"
   • "wasn't" -> "was not"
   • "weren't" -> "were not"
   • "hasn't" -> "has not"
   • "haven't" -> "have not"
   • "wouldn't" -> "would not"
   • "couldn't" -> "could not"
   • "shouldn't" -> "should not"
   • "didn't" -> "did not"
   • "let's" -> "let us"
3. Remove all punctuation (keep only alphanumeric and spaces)
4. Collapse multiple spaces into a single space and strip leading/trailing spaces

Input: A single line of text Output: The normalized text