fuzz-tests: verify round‑trip scriptpubkey <-> addr conversion

Changelog-None: Currently, fuzz-addr only tests encoding via
encode_scriptpubkey_to_addr(), without checking decoding. Add a
round‑trip assertion: if encoding produces an address, decode
it back with decode_scriptpubkey_from_addr() and confirm the
result matches the original scriptpubkey.

Author: Chandra Pratap

tests/fuzz/fuzz-addr.c

@@ -3,6 +3,7 @@
 #include <common/addr.h>
 #include <common/setup.h>
 #include <common/utils.h>
+#include <assert.h>
 #include <tests/fuzz/libfuzz.h>
 
 void init(int *argc, char ***argv)
@@ -15,7 +16,12 @@ void run(const uint8_t *data, size_t size)
 {
 	uint8_t *script_pubkey = tal_dup_arr(tmpctx, uint8_t, data, size, 0);
 
-	encode_scriptpubkey_to_addr(tmpctx, chainparams, script_pubkey);
+	char *addr = encode_scriptpubkey_to_addr(tmpctx, chainparams, script_pubkey);
+	if (addr) {
+		uint8_t *decoded_script_pubkey;
+		assert(decode_scriptpubkey_from_addr(tmpctx, chainparams, addr, &decoded_script_pubkey));
+		assert(tal_arr_eq(script_pubkey, decoded_script_pubkey));
+	}
 
 	clean_tmpctx();
 }