Function canonicalize_code 

pub fn canonicalize_code(code: &str) -> String

Canonicalize code for consistent hashing.

This normalizes whitespace to ensure semantically identical code produces the same hash, regardless of:

• Leading/trailing whitespace or newlines on the whole string
• Trailing whitespace on individual lines
• Windows vs Unix line endings (\r\n vs \n)
• Blank lines between statements