fix(dash): resolve clippy manual_is_multiple_of warnings in special transactions

Replace manual modulo checks with is_multiple_of() method in hex_decode functions:
- coinbase.rs: Check for odd-length hex strings
- mnhf_signal.rs: Check for odd-length hex strings

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: PastaPastaPasta

dash/src/blockdata/transaction/special_transaction/coinbase.rs

@@ -249,7 +249,7 @@ mod tests {
     }
 
     fn hex_decode(s: &str) -> Result<Vec<u8>, &'static str> {
-        if s.len() % 2 != 0 {
+        if !s.len().is_multiple_of(2) {
             return Err("Hex string has odd length");
         }
 

dash/src/blockdata/transaction/special_transaction/mnhf_signal.rs

@@ -154,7 +154,7 @@ mod tests {
     }
 
     fn hex_decode(s: &str) -> Result<Vec<u8>, &'static str> {
-        if s.len() % 2 != 0 {
+        if !s.len().is_multiple_of(2) {
             return Err("Hex string has odd length");
         }