feat: Enhanced recursive parent/child task search | insert [ ] on list

[echaya]

Hey there, me again :)

This PR is meant to allow [ ] automatically inserted on todo.toggle when cursor is on a list line. This was supported in vimwiki and I found it more ergonomics than insert [ ] myself.

During test, I also enhanced parent/child search logic to better handle the structure below

### todo
* [ ] parent
    * [x] child 1
        * some notes
            * some link
    * [ ] child 2
        * [x]  grandchild 1
            * some notes
        * [x] grandchild 2