Store matrix of uint64s values.
It is recommended to store the matrix as a 1D array
because it produces less bytes during serialization than a 2D array.
The matrix does store the number of columns, but it does not store the number of rows.
The number of rows can automatically be calculated as length(data)/n_cols.
{
"nCols": "string",
"data": [
"string"
]
}