⭐ feat: Migrate from WebSocket to libp2p for peer-to-peer connectivity (#286)

## Description
Whew, some stuff is still not re-implemented, but it's working!

Rabbit's gonna explode with the amount of changes I reckon 😅



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced a peer-to-peer relay system using libp2p with enhanced
stream forwarding, room state synchronization, and mDNS peer discovery.
- Added decentralized room and participant management, metrics
publishing, and safe, size-limited, concurrent message streaming with
robust framing and callback dispatching.
- Implemented asynchronous, callback-driven message handling over custom
libp2p streams replacing WebSocket signaling.
- **Improvements**
- Migrated signaling and stream protocols from WebSocket to libp2p,
improving reliability and scalability.
- Simplified configuration and environment variables, removing
deprecated flags and adding persistent data support.
- Enhanced logging, error handling, and connection management for better
observability and robustness.
- Refined RTP header extension registration and NAT IP handling for
improved WebRTC performance.
- **Bug Fixes**
- Improved ICE candidate buffering and SDP negotiation in WebRTC
connections.
  - Fixed NAT IP and UDP port range configuration issues.
- **Refactor**
- Modularized codebase, reorganized relay and server logic, and removed
deprecated WebSocket-based components.
- Streamlined message structures, removed obsolete enums and message
types, and simplified SafeMap concurrency.
- Replaced WebSocket signaling with libp2p stream protocols in server
and relay components.
- **Chores**
- Updated and cleaned dependencies across Go, Rust, and JavaScript
packages.
  - Added `.gitignore` for persistent data directory in relay package.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>
Co-authored-by: Philipp Neumann <3daquawolf@gmail.com>

packages/relay/internal/connections/datachannel.go

@@ -1,12 +1,15 @@
 package connections
 
 import (
-	"github.com/pion/webrtc/v4"
-	"google.golang.org/protobuf/proto"
 	"log/slog"
 	gen "relay/internal/proto"
+
+	"github.com/pion/webrtc/v4"
+	"google.golang.org/protobuf/proto"
 )
 
+type OnMessageCallback func(data []byte)
+
 // NestriDataChannel is a custom data channel with callbacks
 type NestriDataChannel struct {
 	*webrtc.DataChannel
@@ -37,7 +40,7 @@ func NewNestriDataChannel(dc *webrtc.DataChannel) *NestriDataChannel {
 		// Handle message type callback
 		if callback, ok := ndc.callbacks["input"]; ok {
 			go callback(msg.Data)
-		} // TODO: Log unknown message type?
+		} // We don't care about unhandled messages
 	})
 
 	return ndc