Update ExprGameRule

[erenkarakal]

Problem

• isSingle always returns false even if a single value is returned
• Before setting a gamerule, it doesn't check if the gamerule can be assigned to the given value, which prints errors during runtime.

Solution

Fixed the problems and updated the outdated code. Also adds runtime errors for when you use a wrong value for a gamemode (ex. boolean for spawnRadius)

Testing Completed

on load:
  set {_w} to world("world")
  set gamerule spawnRadius of {_w} to 5.3
  broadcast whether gamerule spawnRadius of {_w} is 5

  set gamerule spawnRadius of {_w} to 6
  broadcast whether gamerule spawnRadius of {_w} is 6

  set gamerule doFireTick of {_w} to true
  broadcast whether gamerule doFireTick of {_w} is true

  set {_} to gamerule spawnRadius of {_w}

  # errors
  set gamerule doFireTick of {_w} to 5
  set gamerule spawnRadius of {_w} to true
  set {_} to gamerule spawnRadius of {_w} and {_w}

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Completes: #7939
Related: none

[APickledWalrus]

couple last things