Add mushroom farming

[farooqkz]

• This PR has been tested locally

This PR is a draft because I think it needs more polish. Or it might not need. Reviews are very welcome!

[LoneWolfHT]

What do you get if you time the per-step lua time with (endtime - starttime) / 1e6 using minetest.get_us_time() for the times; Placing a lot of mushrooms to test with?

[farooqkz]

What do you get if you time the per-step lua time with (endtime - starttime) / 1e6 using minetest.get_us_time() for the times; Placing a lot of mushrooms to test with?

Not sure what you mean. Are you suggesting using this method instead of the current method with globalstep? BTW, This PR spawns mushrooms anywhere dark enough. So you don't need mushrooms to farm mushrooms. I think this is better since selfish players could prevent others from farming mushroom. If unsure, we can do a poll.

[LoneWolfHT]

Not sure what you mean. Are you suggesting using this method instead of the current method with globalstep?

What I posted is how you measure how much lag it's causing, by timing how long it takes to get from the start of the globalstep to the end of it