Store: introduce Block_store_status.get_status_value

This simple MR aims to introduce a new Block_store_status getter: get_status_value. This is particularly useful to get the current count of the status, especially in the context of %Non-blocking RPC feature as experimental and !9490 (merged) .

See !9490 (comment 1895813399)

Manually testing the MR

Green CI

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR