Add multi-behavior + disadoption support to rdiffnet_multiple()

[aoliveram]

Hi all — quick note inspired by @DennisNientimp (thanks for the nudge!).

The problem:
rdiffnet_multiple() currently runs multiple simulations for a single behavior only. There’s no built-in way to batch simulations when there are multiple behaviors or to apply disadoption rules across runs, which makes it hard to compare seeding strategies in multi-behavior settings on a static (cross-sectional) network.

What we’d like:
Allow rdiffnet_multiple() to forward multi-behavior inputs to rdiffnet (behavior, per-behavior seed.nodes strategies, thresholds, etc. ).
Accept a disadopt rule (either a single function or a list per behavior) and invoke it per step/run.
Update documentation.
Add more tests to rdiffnet_multiple().

This way we could run side-by-side simulation studies (e.g., random vs central seeding) with more than one behavior and optional disadoption, without writing custom wrappers that use rdiffnet().