Investigate performance effects of current structure

## Motivation:
Every convenience comes at a cost, but quantifying the cost makes it possible to determine whether it's "too expensive".

## Suggested Method
Currently use a combination of inheritance and composition, which make modification and new base classes really simple to implement and use, but may come at a performance cost. Would be good to quantify the difference between the current situation and e.g. the 'best-case' performance of `VideoReader`, `LockedCamera`, and `LockedScreen` being implemented with `cv2.VideoCapture` as their direct parent class.

## Possible Resulting Changes
If performance difference is significant, it may be worth
- making a code-generator that can trade off some program memory for the benefit of fewer function calls at each step
- changing code structure (hard to recommend - very versatile at the moment, and repetition is a 'bad smell')
- recommending this library for rapid development, and more optimised code once development is complete (e.g. lower level looping, or just C++ implementation)