Allow uppercase bech32 HRP

Previously, we would fail parsing `Offer`s if the HRP didn't match our
expected (lowercase) HRP. Here, we relax this check in accordance with
the spec to also allow all-uppercase HRPs.

Author: tnull

lightning/src/offers/parse.rs

@@ -58,7 +58,8 @@ mod sealed {
 
 			let parsed = CheckedHrpstring::new::<NoChecksum>(encoded.as_ref())?;
 			let hrp = parsed.hrp();
-			if hrp.as_str() != Self::BECH32_HRP {
+			// Compare the lowercase'd iter to allow for all-uppercase HRPs
+			if hrp.lowercase_char_iter().ne(Self::BECH32_HRP.chars()) {
 				return Err(Bolt12ParseError::InvalidBech32Hrp);
 			}