refactor: Replace HexStr(o.begin(), o.end()) with HexStr(o)

HexStr can be called with anything that bas `begin()` and `end()` functions,
so clean up the redundant calls.

src/test/fuzz/key.cpp

@@ -108,7 +108,7 @@ void test_one_input(const std::vector<uint8_t>& buffer)
         assert(pubkey.IsCompressed());
         assert(pubkey.IsValid());
         assert(pubkey.IsFullyValid());
-        assert(HexToPubKey(HexStr(pubkey.begin(), pubkey.end())) == pubkey);
+        assert(HexToPubKey(HexStr(pubkey)) == pubkey);
         assert(GetAllDestinationsForKey(pubkey).size() == 3);
     }