Add onread callback

src/reader.ts

@@ -54,6 +54,7 @@ export class Reader {
 			}
 		}
 
+		this.source.onread?.({ start, end });
 		const bytesPromise = this.source._read(start, end);
 		const loadingSegment: LoadingSegment = { start, end, promise: bytesPromise };
 		this.loadingSegments.push(loadingSegment);

src/source.ts

@@ -12,6 +12,8 @@ export abstract class Source {
 	_getSize() {
 		return this._sizePromise ??= this._retrieveSize();
 	}
+
+	onread: ((range: { start: number; end: number }) => unknown) | null = null;
 }
 
 /** @public */