Add Plugin Lifecycle Hooks before/after each <py-script> tag executes

[JeffersGlass]

From a discussion on the Discord - for the purposes of enabling functionality around each PyScript tag, it would be nice to have a before-py-script and after-py-script lifecycle hook that execute immediately before and after each tag is evaluated. (Names suggested by @antocuni and are flexible.)

Some possible use-cases are:

• Allowing redirection of stdout for each tag separately
• Simple profiling by timing the execution of each tag
• A tag-oriented "debugger" which pauses the execution of PyScript tags in between each tags, to allow the user to observe what that specific tag did.

Not that these are perfect (or fully-fleshed-out) examples, but an idea of what might be possible.