Fix: Incorrect when dealing with UTF-8 chars > 1 byte

[WardLordRuby]

Calling .len() on a String or &str in rust returns the byte length.

Also fixed the clippy lint.

• File(s) Modified: 0271-encode-and-decode-strings.rs
• Language(s) Used: rust
• Submission URL: https://github.com/WardLordRuby/leetcode-fix-rust-0271/commit/7808e8d313e640f052514c8e2826117ae74c5be6?diff=unified&w=1