paste method
Copy this with the other world pasted in at the given location.
Result will be large enough to contain both.
Implementation
GridWorld paste(final int cI, final int cJ, final GridWorld other) =>
GridWorld.empty(
max(_numRows, cI + other.nRows), max(_numCols, cJ + other.nCols))
.._paste(0, 0, this)
.._paste(cI, cJ, other);