⭐ 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/common/crypto.go

@@ -1,19 +1,51 @@
 package common
 
 import (
+	"crypto/ed25519"
 	"crypto/rand"
-	"crypto/sha256"
-	"github.com/oklog/ulid/v2"
+	"errors"
+	"fmt"
+	"os"
 	"time"
+
+	"github.com/oklog/ulid/v2"
 )
 
 func NewULID() (ulid.ULID, error) {
 	return ulid.New(ulid.Timestamp(time.Now()), ulid.Monotonic(rand.Reader, 0))
 }
 
-// Helper function to generate PSK from token
-func GeneratePSKFromToken(token string) ([]byte, error) {
-	// Simple hash-based PSK generation (32 bytes for libp2p)
-	hash := sha256.Sum256([]byte(token))
-	return hash[:], nil
+// GenerateED25519Key generates a new ED25519 key
+func GenerateED25519Key() (ed25519.PrivateKey, error) {
+	_, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate ED25519 key pair: %w", err)
+	}
+	return priv, nil
+}
+
+// SaveED25519Key saves an ED25519 private key to a path as a binary file
+func SaveED25519Key(privateKey ed25519.PrivateKey, filePath string) error {
+	if privateKey == nil {
+		return errors.New("private key cannot be nil")
+	}
+	if len(privateKey) != ed25519.PrivateKeySize {
+		return errors.New("private key must be exactly 64 bytes for ED25519")
+	}
+	if err := os.WriteFile(filePath, privateKey, 0600); err != nil {
+		return fmt.Errorf("failed to save ED25519 key to %s: %w", filePath, err)
+	}
+	return nil
+}
+
+// LoadED25519Key loads an ED25519 private key binary file from a path
+func LoadED25519Key(filePath string) (ed25519.PrivateKey, error) {
+	data, err := os.ReadFile(filePath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read ED25519 key from %s: %w", filePath, err)
+	}
+	if len(data) != ed25519.PrivateKeySize {
+		return nil, fmt.Errorf("ED25519 key must be exactly %d bytes, got %d", ed25519.PrivateKeySize, len(data))
+	}
+	return data, nil
 }