[IoT State Channels] Adapt perun-rs implementation to use remote interfaces of perun-node

#### Motivation / Context

Align the remote interfaces used by perun-rs and perun-node.

#### Description

Currently, the embedded library "perun-rs" uses a custom implementation of remote watching and remote funder. Adapt the implementation to use the interfaces implemented by perun-node.

##### Relates to

#### Testing

Make a demonstrator making transactions between perun-rs client and perun-node (which uses go-perun).

#### Thread Safety

NA