Function percent_encode 

pub fn percent_encode(input: &str) -> String

What: Percent-encode a string for use in URLs according to RFC 3986.

Inputs:

• input: String to encode.

Output:

• Returns a percent-encoded string where reserved characters are escaped.

Details:

• Unreserved characters as per RFC 3986 (A-Z, a-z, 0-9, -, ., _, ~) are left as-is.
• Space is encoded as %20 (not +).
• All other bytes are encoded as two uppercase hexadecimal digits prefixed by %.
• Operates on raw bytes from the input string; any non-ASCII bytes are hex-escaped.