fix(blocks): add slug name to error messaging for block type/schema fetch failure

[parkedwards]

when an incorrect slug is provided, the error can be hard to track down. to help, we'll print the slug itself in the error message

this is the current error message

Could not get_by_slug Block Type, unexpected error: All attempts fail:
#1: status code 404 Not Found, error={"detail":"Block type not found"}