Epic: Simplify the OONI Probe engine

[hellais]

This goal of this epic is to keep track of all the work related to simplifying the engine.

The idea is to remove any code for features which are too costly to continue maintaining and as part of that take some opportunities to reduce the codebase where possible.

The high level goals we put for this target are:

• Simplify or eliminate the forks of go/crypto and go/http
• Reduce the number of ways we write experiments
• Make it possible to not have to release engine versions so often
• Externalize the geoip dependencies outside of the engine
  • Get rid of asset embedding and updating
• Expose an API that’s more “useful” to mobile developers (see: https://docs.google.com/document/d/1gY31ewo-vCieiIxvm_PwOQd01z_AW-7YIh5nlifJN98/edit?tab=t.0#heading=h.1wtg5jpckjek)
• OONI Run v2 might be merged with richer input related code
• Solve integration of rust libraries such as arti
• Reduce overall Probe engine codebase (current clocked at ~56k LoC)

More details about this rational and other history is present in this design doc: https://docs.google.com/document/d/1CDYNleCcz9uywsuo8k0U1W46SuJQFLvpl9jYU1VJaR8/edit?tab=t.0#heading=h.jdo6dlokobzv