Add comprehensive test coverage for core functionalities

This commit introduces test cases for the API, archive, store, and filesystem functionalities, as well as a functional test for a full workflow. It ensures robust testing for snapshot operations, archiving, and blob management, significantly improving reliability.

store/errors.go

@@ -0,0 +1,9 @@
+package store
+
+import "errors"
+
+// Common errors that can be used by store implementations
+var (
+	// ErrNotFound means that a requested resource was not found
+	ErrNotFound = errors.New("resource not found")
+)