refactor: Split dbwrapper CDBWrapper::Read implementation

Keep the generic serialization in the header, while moving
leveldb-specifics to the implementation file.

The context of this commit is an effort to decouple the dbwrapper header
file from leveldb includes. To this end, the includes are moved to the
dbwrapper implementation file. This is done as part of the kernel
project to reduce the number of required includes for users of the
kernel.

Author: TheCharlatan

src/dbwrapper.cpp

@@ -10,7 +10,6 @@
 #include <serialize.h>
 #include <span.h>
 #include <streams.h>
-#include <tinyformat.h>
 #include <util/fs.h>
 #include <util/fs_helpers.h>
 #include <util/strencodings.h>
@@ -300,6 +299,20 @@ std::vector<unsigned char> CDBWrapper::CreateObfuscateKey() const
     return ret;
 }
 
+std::optional<std::string> CDBWrapper::ReadImpl(Span<const std::byte> ssKey) const
+{
+    leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
+    std::string strValue;
+    leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
+    if (!status.ok()) {
+        if (status.IsNotFound())
+            return std::nullopt;
+        LogPrintf("LevelDB read failure: %s\n", status.ToString());
+        dbwrapper_private::HandleError(status);
+    }
+    return strValue;
+}
+
 bool CDBWrapper::IsEmpty()
 {
     std::unique_ptr<CDBIterator> it(NewIterator());

src/dbwrapper.h

@@ -235,6 +235,8 @@ class CDBWrapper
     //! whether or not the database resides in memory
     bool m_is_memory;
 
+    std::optional<std::string> ReadImpl(Span<const std::byte> ssKey) const;
+
 public:
     CDBWrapper(const DBParams& params);
     ~CDBWrapper();
@@ -248,18 +250,12 @@ class CDBWrapper
         DataStream ssKey{};
         ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
         ssKey << key;
-        leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
-
-        std::string strValue;
-        leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
-        if (!status.ok()) {
-            if (status.IsNotFound())
-                return false;
-            LogPrintf("LevelDB read failure: %s\n", status.ToString());
-            dbwrapper_private::HandleError(status);
+        std::optional<std::string> strValue{ReadImpl(ssKey)};
+        if (!strValue) {
+            return false;
         }
         try {
-            CDataStream ssValue{MakeByteSpan(strValue), SER_DISK, CLIENT_VERSION};
+            CDataStream ssValue{MakeByteSpan(*strValue), SER_DISK, CLIENT_VERSION};
             ssValue.Xor(obfuscate_key);
             ssValue >> value;
         } catch (const std::exception&) {