Normalize a file path

Given an absolute Unix-style file path as a string, return its canonical normalized form. Rules: - The input always starts with `/`. - A single `.` means the current directory and should be ignored. - A double dot `..` means move to the parent directory if possible. - Multiple consecutive slashes should be treated as a single slash. - The output must: - start with exactly one `/` - contain directory names separated by a single slash - not end with a trailing slash unless the result is the root path `/` Example: - Input: `/a//b/./c/../d/` - Output: `/a/b/d` Explain your approach and implement the function.