Add experimental_remote_packages config flag for remote packages

[WebReflection]

In our latest Community Call I've demoed a PoC around the proposal that would allow users to provide their own PyScript packages with extreme ease.

The scope of the proposal is wider than this MR, but in here I would like to enable experiments, feedback, and whatnot, around this possibility, so here what's backed in:

• only if experimental_remote_packages = true or truthy equivalent, the rest of the logic applies
• if within the packages list there is something ending with either .toml or .json, that package is parsed and merged into current config/logic
• differently from the PoC code, this works for both Pyodide and MicroPython interpreters
• differently from the PoC code, this throws if things are off (same name, different remote package, or already solved name, and so on) ... this is to have a base to explore with issues that fail fast and allow us to eventually relax that in the future
• differently from the PoC code, this now avoid parsing same nested dependencies over and over, so it's recursion-aware out of the box

A basic example to explain how this work:

experimental_remote_packages = true

packages = ['https://webreflection.github.io/examples/pyscript/module/package.toml']

This has been tested and it's working wonderfully for the little that foreign module does, but as an opt-in experimental starting point, I think we should push this possibility forward and react accordingly after feedback.

[ntoll]

Yes, for feedback purposes. 👍