Support multiple pixel shaders to be applied on the terminal texture buffer

# Allow multiple pixel shaders to be specified

Current configuration allows the user to specify a single pixel shader. It'd be useful if the parameter could be a list of shaders to be applied in order, for instance, distorting the screen to make it match a CRT tube (could be be even specified as two shaders, one for horizontal curvature that, if applied alone, would simulate a Trinitron tube, and other for the vertical curvature) and another to simulate raster artifacts.

# Proposed technical implementation details (optional)

I'd keep the current syntax that accepts a single string for single shaders, and also accept a list of strings for multiple shaders to be applied in order.

No files or tests are named. Start by locating the current configuration entry point for the single pixel shader and the terminal texture buffer rendering path. Confirm how shaders are loaded and applied, then verify that a list preserves shader order while retaining the existing single-string behavior.

Written by the indexing model from the issue text.