validation: Apply fixes for Bitcoin backport compliance

- Remove unnecessary std::string() conversions in ParseHashO and ParseHexO
- Change ParseHashV variable declaration to match Bitcoin's const reference style
- Add missing blank line after #include <tuple>

These changes ensure the backport matches Bitcoin commit 9b68c9b exactly.

Author: claude

pyenv

@@ -0,0 +1 @@
+Subproject commit 61d869f67e2b4c1d05c532821c5166a9ed40b0aa

src/rpc/util.cpp

@@ -19,6 +19,7 @@
 
 #include <string_view>
 #include <tuple>
+
 const std::string UNIX_EPOCH_TIME = "UNIX epoch time";
 const std::string EXAMPLE_ADDRESS[2] = {"XunLY9Tf7Zsef8gMGL2fhWA9ZmMjt4KPw0", "XwQQkwA4FYkq2XERzMY2CiAZhJTEDAbtc0"};
 
@@ -101,7 +102,7 @@ CAmount AmountFromValue(const UniValue& value, int decimals)
 
 uint256 ParseHashV(const UniValue& v, std::string_view name)
 {
-    std::string strHex{v.get_str()};
+    const std::string& strHex(v.get_str());
     if (64 != strHex.length())
         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("%s must be of length %d (not %d, for '%s')", name, 64, strHex.length(), strHex));
     if (!IsHex(strHex)) // Note: IsHex("") is false
@@ -110,7 +111,7 @@ uint256 ParseHashV(const UniValue& v, std::string_view name)
 }
 uint256 ParseHashO(const UniValue& o, std::string_view strKey)
 {
-    return ParseHashV(o.find_value(std::string(strKey)), strKey);
+    return ParseHashV(o.find_value(strKey), strKey);
 }
 std::vector<unsigned char> ParseHexV(const UniValue& v, std::string_view name)
 {
@@ -123,7 +124,7 @@ std::vector<unsigned char> ParseHexV(const UniValue& v, std::string_view name)
 }
 std::vector<unsigned char> ParseHexO(const UniValue& o, std::string_view strKey)
 {
-    return ParseHexV(o.find_value(std::string(strKey)), strKey);
+    return ParseHexV(o.find_value(strKey), strKey);
 }
 
 int32_t ParseInt32V(const UniValue& v, const std::string &strName)