feat(util/lazy_list): add repeat and repeat_at_most templates for lazy_lists

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/tactic): refine repeat and repeat_at_most tacticals

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/tactic): minimize the amount of copying in the tactic API

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>