Implement `NetworkBitStream`

[ikkentim]

NetworkBitStream has not been implemented yet in the .Core library.

This type is used for handling OnReceive/OnSend of network packets and RPCs.

[bssth]

Real blocker is that NetworkBitStream lives in open.mp/Shared/Network/bitstream.hpp, not in open.mp-sdk. The SDK only has a forward declaration, so the native component can't call any of its methods - the event handlers pass NetworkBitStream& through as an opaque pointer.

Two ways forward:

1. Vendor bitstream.hpp + bitstream.cpp into sampsharp-component. Self-contained, lands independently.
2. Get bitstream upstreamed into open.mp-sdk. Cleaner, but waits on open.mp maintainers.

Maybe I'm wrong but it looks like this

[ikkentim]

We could simply add another submodule. But this is low priority. It's not essential