Make unbounded channels explicit.

We used to have unbounded channels embedded within rtpconn
and webClient.  Make the structure explicit and testable.

unbounded/unbounded.go

@@ -0,0 +1,47 @@
+package unbounded
+
+import (
+	"sync"
+)
+
+// Type Channel implements an unbounded channel
+type Channel[T any] struct {
+	// Ch triggers whenever the channel becomes non-empty
+	Ch chan struct{}
+
+	mu    sync.Mutex
+	queue []T
+}
+
+// New creates a new unbounded channel
+func New[T any]() *Channel[T] {
+	return &Channel[T]{
+		Ch: make(chan struct{}, 1),
+	}
+}
+
+// Put inserts a new element into ch.
+// If ch was previously empty, it triggers ch.Ch.
+func (ch *Channel[T]) Put(v T) {
+	ch.mu.Lock()
+	empty := len(ch.queue) == 0
+	ch.queue = append(ch.queue, v)
+	ch.mu.Unlock()
+
+	if empty {
+		select {
+		case ch.Ch <- struct{}{}:
+		default:
+		}
+	}
+}
+
+// Get removes all the elements of ch.
+// It is usually called when ch.Ch triggers, but may be called at any time.
+func (ch *Channel[T]) Get() []T {
+	ch.mu.Lock()
+	defer ch.mu.Unlock()
+	queue := ch.queue
+	ch.queue = nil
+	return queue
+}