refactor: commit to 8 byte obfuscation keys

Since 31 byte xor-keys are not used in the codebase, using the common size (8 bytes) makes the benchmarks more realistic.

Co-authored-by: maflcko <6399679+maflcko@users.noreply.github.com>

src/node/blockstorage.cpp

@@ -31,6 +31,7 @@
 #include <util/batchpriority.h>
 #include <util/check.h>
 #include <util/fs.h>
+#include <util/obfuscation.h>
 #include <util/signalinterrupt.h>
 #include <util/strencodings.h>
 #include <util/syserror.h>
@@ -1123,7 +1124,7 @@ static auto InitBlocksdirXorKey(const BlockManager::Options& opts)
 {
     // Bytes are serialized without length indicator, so this is also the exact
     // size of the XOR-key file.
-    std::array<std::byte, 8> xor_key{};
+    std::array<std::byte, Obfuscation::KEY_SIZE> xor_key{};
 
     // Consider this to be the first run if the blocksdir contains only hidden
     // files (those which start with a .). Checking for a fully-empty dir would