miniscript: add an OpCode typedef for readability

Suggested-by: Vincenzo Palazzo

Author: darosior

src/script/miniscript.cpp

@@ -281,9 +281,9 @@ size_t ComputeScriptLen(Fragment fragment, Type sub0typ, size_t subsize, uint32_
     return 0;
 }
 
-std::optional<std::vector<std::pair<opcodetype, std::vector<unsigned char>>>> DecomposeScript(const CScript& script)
+std::optional<std::vector<Opcode>> DecomposeScript(const CScript& script)
 {
-    std::vector<std::pair<opcodetype, std::vector<unsigned char>>> out;
+    std::vector<Opcode> out;
     CScript::const_iterator it = script.begin(), itend = script.end();
     while (it != itend) {
         std::vector<unsigned char> push_data;
@@ -317,7 +317,7 @@ std::optional<std::vector<std::pair<opcodetype, std::vector<unsigned char>>>> De
     return out;
 }
 
-std::optional<int64_t> ParseScriptNumber(const std::pair<opcodetype, std::vector<unsigned char>>& in) {
+std::optional<int64_t> ParseScriptNumber(const Opcode& in) {
     if (in.first == OP_0) {
         return 0;
     }

src/script/miniscript.h

@@ -180,6 +180,8 @@ inline constexpr Type operator"" _mst(const char* c, size_t l) {
     return typ;
 }
 
+using Opcode = std::pair<opcodetype, std::vector<unsigned char>>;
+
 template<typename Key> struct Node;
 template<typename Key> using NodeRef = std::shared_ptr<const Node<Key>>;
 
@@ -1269,10 +1271,10 @@ inline NodeRef<Key> Parse(Span<const char> in, const Ctx& ctx)
  * and OP_EQUALVERIFY are decomposed into OP_CHECKSIG, OP_CHECKMULTISIG, OP_EQUAL
  * respectively, plus OP_VERIFY.
  */
-std::optional<std::vector<std::pair<opcodetype, std::vector<unsigned char>>>> DecomposeScript(const CScript& script);
+std::optional<std::vector<Opcode>> DecomposeScript(const CScript& script);
 
 /** Determine whether the passed pair (created by DecomposeScript) is pushing a number. */
-std::optional<int64_t> ParseScriptNumber(const std::pair<opcodetype, std::vector<unsigned char>>& in);
+std::optional<int64_t> ParseScriptNumber(const Opcode& in);
 
 enum class DecodeContext {
     /** A single expression of type B, K, or V. Specifically, this can't be an