ENH: Redesign of the Extension [Major Change]

[AakashGfude]

This is a rewrite of the extension to incorporate lessons learnt and to remove some of the path dependant decisions that were made as features were added over time.

This update includes:

1. execution as a separate builder pipeline. This executes all the code blocks and stores them as a .codetree files for use by all jupyter builders. This will allow single execution across the various build targets. The output saved in the .codetree file for the respective code block is merged with the .ipynb file produced.
2. The builders and translators are now independent for each target (ipynb, pdf, html). Adding features for the various output types will not have possible regressions against other output types due to the previously unified translator.