test(utils): Add test and error handling for wiped InMemorySecret

- Updated `InMemorySecret.get_bytes()` in `src/utils/memory_protection.py` to raise a `RuntimeError` if the secret has been wiped, replacing the previous `AttributeError`.
- Added `test_access_after_wipe_raises_error` to `src/tests/test_memory_protection.py` to verify this behavior.

Co-authored-by: PR0M3TH3AN <[email protected]>

src/utils/memory_protection.py

@@ -17,6 +17,8 @@ class InMemorySecret:
 
     def get_bytes(self) -> bytes:
         """Decrypt and return the plaintext bytes."""
+        if self._cipher is None:
+            raise RuntimeError("Secret has been wiped")
         return self._cipher.decrypt(self._nonce, self._encrypted, None)
 
     def wipe(self) -> None: