Changing RouterContext.netDb() return type is a breaking API change

Not familiar with the MR !101 (merged) history but I see it has 168 commits over 3 months so it's not really feasible for me to review the history and discussions.

But changing the return type of RouterContext.netDb() from FNDF to FNDS (Segmentor) is a breaking API change (whether FNDS extends FNDF or not, which it currently does not) to a 20-year-old API.

This will break any bundlers or plugins that access netDb(). While external uses of RouterContext should be much much less than I2PAppContext, still, this is a major breakage that of the type that we almost never do, and shouldn't be done lightly. It's quite disruptive, and I see it was disruptive in-tree as well, as MR !101 (merged) changes 103(!) files.

Again, I don't know if you already considered these issues and possible alternatives, reviewed all known plugins and bundlers (and android) and decided to go down this path. But I'm entering this ticket to ask if you're absolutely sure you want to do it this way.