End-to-end test Mineflayer bots without Java using flying-squid

When no Java is installed, you can still run a Mineflayer bot end to end against flying-squid (PrismarineJS's Node Minecraft server, supports up to ~1.21.4): createMCServer with 'online-mode': false and superflat generation, then point the bot at its port. Install it in a scratch dir and set NODE_PATH rather than adding it to the project. The full-system run caught a bug unit tests with a fake bot missed: a raycast 'obstacle ahead' check that used the bottom row of a downward-fanned eye grid kept hitting the floor, so the agent jumped every tick; use the eye-level row instead. Also, when stopping background servers, pkill -f <pattern> can match and kill your own shell if the pattern appears in the command line; use pkill -f '[m]ypattern' and avoid launching and killing in the same command.