Branch mine

Wow this literally hasn't been suggested before? tf

## Describe your suggestion
Okay so legitmine was made with the principle that it would make you look more legit to admins.
In all honesty that's a load of baloney. If I'm watching a player and they xray towards a cave, and take specific directions to go to a small block of diamond that was outcropped, that's sus af.

Branchmine would do literally that: branchmine. Dig down to Y=11, dig a tunnel - trace back, dig that way. Then come back in the middle, move 3 blocks to forward, repeat. Get any ores that crop up in the middle. Maybe even fill in the tunnels with a single block at the hallway to keep creepers from coming back in at you.


## Settings
Distances the branches go, space between branches, what Y level, how wide the "main shaft" should be.

## Context

You're not going to find all of the diamonds everywhere. You're not expected to - that's sus. Your goal is to mine like a legit human so that when people ask you where you got 2 stacks of diamonds, you can show them the mines under your base and the miles of branch-mining.

## Final checklist
- [x] I have not used any OwO's or UwU's in this issue.

No files, tests, or entry points are named. Start by locating the existing legitmine behavior and the mining command or subsystem, then compare its configuration patterns with the requested branch distances, spacing, Y level, shaft width, ore collection, and tunnel filling. Done means branch mining follows those settings while remaining intentionally human-like.

Written by the indexing model from the issue text.