scripts: lint: Handle store connections for lint checkers.

scripts: lint: Handle store connections for lint checkers.

Rather than individual checkers opening up a connection to the store for each
package to check, if any checker requires a store connection, open a
connection and pass it to all checkers that would use it. This makes running
the derivation checker much faster for multiple packages.

* guix/scripts/lint.scm (run-checkers): Add a #:store argument, and pass the
store to checkers if they require a store connection.
(guix-lint): Establish a store connection if any checker requires one, and
pass it through to run-checkers.