Add rate limiting for import

**Description**
Currently store lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

No file, test, or entry point is named, and the title conflicts with the body. First clarify whether the requested change is import rate limiting or configurable store serialization, then locate the relevant store or import entry point and existing tests. Done means the confirmed behavior is configurable, has sensible defaults, and is covered by tests.

Written by the indexing model from the issue text.