refactor: Hand-replace some ParseHex -> ""_hex

The following scripted-diff commit will replace ParseHex("...") with "..."_hex_u8, but this replacement will not work in cases where vectors are needed instead of arrays, and is not ideal in cases where std::byte is accepted.

For example, it is currently necessary to use _hex_v_u8 when calling CScript operator<< because that operator does not currently support std::array or std::byte.

Conversely, it is incorrect to use _hex_v instead of _hex in net_processing.cpp for the MakeAndPushMessage argument, because if the argument is a std::vector it is considered variable-length and serialized with a size prefix, but if the argument is a std::array or Span is it considered fixed length and serialized without a prefix.

By the same logic, it is also safe to change the NUMS_H constant in pubkey.cpp from a std::vector to std::array because it is never serialized.

src/test/script_tests.cpp

@@ -35,6 +35,8 @@
 // Uncomment if you want to output updated JSON tests.
 // #define UPDATE_JSON_TESTS
 
+using namespace util::hex_literals;
+
 static const unsigned int gFlags = SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_STRICTENC;
 
 unsigned int ParseScriptFlags(std::string strFlags);
@@ -1413,7 +1415,7 @@ BOOST_AUTO_TEST_CASE(script_FindAndDelete)
     // prefix, leaving 02ff03 which is push-two-bytes:
     s = ScriptFromHex("0302ff030302ff03");
     d = ScriptFromHex("03");
-    expect = CScript() << ParseHex("ff03") << ParseHex("ff03");
+    expect = CScript() << "ff03"_hex_v_u8 << "ff03"_hex_v_u8;
     BOOST_CHECK_EQUAL(FindAndDelete(s, d), 2);
     BOOST_CHECK(s == expect);