ability to scale the size of cells up and down

[kfarr]

As a user creating or viewing a citybuilderjr scene in mixed reality I wish to be able to choose a custom scale size for all cells in my scene.

The default size of each cell is 0.25 meters (~9.8 inches) and is manually specified in various places:

• snapping logic: https://github.com/3DStreet/citybuilderjr/blob/main/src/app/grid-cursor.js#L79
• voxel size: https://github.com/3DStreet/citybuilderjr/blob/main/src/app/grid-cursor.js#L79
• cursor size: https://github.com/3DStreet/citybuilderjr/blob/main/index.html#L59
• city hall scale: https://github.com/3DStreet/citybuilderjr/blob/main/index.html#L69C1-L70C1
• primitive and snap: https://github.com/3DStreet/citybuilderjr/blob/main/index.html#L77

Instead, perhaps cell size should be a state variable to which these component properties are bound. This would be a global change that affects all cells -- cells should not be allowed to be different sizes.