resize() allocates new objects for each cell

[lordmauve]

TerminalSession.resize() allocates a new grid using a for loop to construct (Style(), " ") tuples.

This is necessary for mutable objects but slow. Resizing a grid to 1000x1000 must allocate 2M objects or more. Because the tuple, the string and the Style are immutable, it would be better to allocate with

grid = [
    [(Style(), " ")] * width
    for row in range(height)
]