feat: speed up cache operations with optimized encryption

Cache load/save operations now complete in milliseconds instead of
hundreds of milliseconds, making transaction syncs noticeably faster
while maintaining full AES-GCM security.

Cargo.toml

@@ -37,7 +37,9 @@ http = "0.2"
 task-local-extensions = "0.1"
 aes-gcm = "0.10"
 pbkdf2 = "0.12"
+hkdf = "0.12"
 rand = "0.8"
 sha2 = "0.10"
 temp-env = "0.3"
 dialoguer = "0.12"
+walkdir = "2.4"