refactor: Split dbwrapper CDBIterator::Seek 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

@@ -306,6 +306,12 @@ bool CDBWrapper::IsEmpty()
     return !(it->Valid());
 }
 
+void CDBIterator::SeekImpl(Span<const std::byte> ssKey)
+{
+    leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
+    piter->Seek(slKey);
+}
+
 CDBIterator::~CDBIterator() { delete piter; }
 bool CDBIterator::Valid() const { return piter->Valid(); }
 void CDBIterator::SeekToFirst() { piter->SeekToFirst(); }

src/dbwrapper.h

@@ -140,6 +140,8 @@ class CDBIterator
     const CDBWrapper &parent;
     leveldb::Iterator *piter;
 
+    void SeekImpl(Span<const std::byte> ssKey);
+
 public:
 
     /**
@@ -158,8 +160,7 @@ class CDBIterator
         DataStream ssKey{};
         ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
         ssKey << key;
-        leveldb::Slice slKey(CharCast(ssKey.data()), ssKey.size());
-        piter->Seek(slKey);
+        SeekImpl(ssKey);
     }
 
     void Next();