Legitmine for a Selection (#sel)

## Describe your suggestion
This expands on the #sel command by adding a way to legitmine in the selection I have and that selection only. So basically, I select a region and then legitmine in that region only.

## Settings
Just like there is a "#sel replace block with block", this could also add a functionality called "#sel mine". If legitmine is activated, then "#sel mine" will do what legitmine does, just inside the selected area. If not, "#sel mine" will do what "#sel replace" does, but with the added ability to specify more than one ore to mine.

## Context
I am currently making a perimeter in Minecraft. I want to be able to mine out the ores the TNT machine reveals, and those ores only. However, the TNT machine also reveals a lot of caves and ravines. #mine gets confused and starts heading down the caves. I came back from being AFK and found that my player was hundreds of blocks away from where I wanted to mine. And also, I know plenty of people who could benefit from something like this. Want to mess with your friends by using automine in a game that has a limited area to mine for ores? Then this #sel legitmine will come in handy.

## Final checklist
- [x] I know how to properly use checkboxes
- [x ] I have not used any OwO's or UwU's in this issue.

Start by reading the existing #sel and #mine command entry points and how selection boundaries are represented. Determine how legitmine currently chooses targets and how #sel replace behaves. Done means #sel mine limits legitmine to the selected region, while the inactive behavior supports replacing blocks with multiple specified ores.

Written by the indexing model from the issue text.