BIG cursor progress

- Add extensive tests for packet cursor, sample cursor, and call serialization
- Major PacketCursor refactor
- Add PacketReader
- Many SampleCursor fixes, harden the behavior
- Typo fixes and various other small things

src/sample.ts

@@ -53,6 +53,9 @@ export type VideoSampleInit = {
  * @public
  */
 export class VideoSample implements Disposable {
+	/** @internal */
+	static _openSampleCount = 0;
+
 	/** @internal */
 	_data!: VideoFrame | OffscreenCanvas | Uint8Array | null;
 	/** @internal */
@@ -107,6 +110,14 @@ export class VideoSample implements Disposable {
 		return this.format && this.format.includes('A');
 	}
 
+	/**
+	 * Whether this sample is closed, meaning its underlying data has been discarded. When a sample is closed, most
+	 * operations will fail.
+	 */
+	get closed() {
+		return this._closed;
+	}
+
 	/**
 	 * Creates a new {@link VideoSample} from a
 	 * [`VideoFrame`](https://developer.mozilla.org/en-US/docs/Web/API/VideoFrame). This is essentially a near zero-cost
@@ -265,6 +276,8 @@ export class VideoSample implements Disposable {
 		} else {
 			throw new TypeError('Invalid data type: Must be a BufferSource or CanvasImageSource.');
 		}
+
+		VideoSample._openSampleCount++;
 	}
 
 	/** Clones this video sample. */
@@ -320,6 +333,7 @@ export class VideoSample implements Disposable {
 		}
 
 		this._closed = true;
+		VideoSample._openSampleCount--;
 	}
 
 	/** Returns the number of bytes required to hold this video sample's pixel data. */
@@ -888,6 +902,14 @@ export class AudioSample implements Disposable {
 		return Math.trunc(SECOND_TO_MICROSECOND_FACTOR * this.duration);
 	}
 
+	/**
+	 * Whether this sample is closed, meaning its underlying data has been discarded. When a sample is closed, most
+	 * operations will fail.
+	 */
+	get closed() {
+		return this._closed;
+	}
+
 	/**
 	 * Creates a new {@link AudioSample}, either from an existing
 	 * [`AudioData`](https://developer.mozilla.org/en-US/docs/Web/API/AudioData) or from raw bytes specified in