FR: repetition counts for + and -

[Zoybean]

Is your feature request related to a problem? Please describe.
Most often when I'm undoing something, I'll look at the op log and then figure out the number of operations I want to undo, then count that many -'s, e.g.: jj op restore @---.
I rarely have a use for more than 2 + or -, outside of jj op restore.

Describe the solution you'd like
I'd like to be able to say jj op restore @-3.
Naturally, this feature would allow both + and - operations to accept a nonnegative integer count, on arbitrary revsets.
Unfortunately, if these are handled as postfix operators, I figure this would imply that things like @-3+2 and pathological combinations like @--3+2++0-+ would be valid syntax, which I think are not desirable, but may be necessary in order for the feature to work.

Describe alternatives you've considered
I could just copy the hash of the state I want to revert to, or continue to count repetitions of + and -. This avoids over-complicating the syntax for such a small gain.

[yuja]

Related: #3337

For op restore specifically, some interactive UI to pick from the last ~10 operations might be useful. Maybe that can also be achieved by using fzf. https://github.com/martinvonz/jj/wiki/fzf

[Zoybean]

Closing in favour of related issues