When mining blocks that are trapped, they are not saved as trapped, so they are revisited again

## Some information
Operating system: Win 10
Java version: v8u45
Minecraft version: 1.14.4 (no impact)
Baritone version: recent (~10 days)(sorry XD)
Forge mods (if used): none

When mining for diamonds, I came across some blocks (diamonds) that were trapped in bedrock. I visited them, and the bot calculated that they were unreachable. However, when i returned to the same area, it tried to pathfind to the diamonds again, even though they were unreachable. This is also quite alot of time wasted, if you are on a not too long mining session where you have cleared out alot of ores around you.

A fix for this could be that if a setting is turned on, unreachable blocks are saved as unreachable, so you don't waste your time revisiting them. Thanks!

No files, tests, or entry points are named. Start by tracing the block-mining pathfinding flow for unreachable diamond blocks and where revisitation is decided; done means an opt-in setting prevents known-unreachable targets from being retried.

Written by the indexing model from the issue text.