hs: Schedule mainloop event on dirinfo change

Due to a possible Guard subsystem recursion, when the HS client gets
notified that the directory information has changed, it must run it in a
seperate mainloop event to avoid such issue.

See the ticket for more information on the recursion. This also fixes a
fatal assert.

Fixes #40579

Signed-off-by: David Goulet <dgoulet@torproject.org>