peekVLQ() {
        const pos = this.#position;
        try {
            return this.nextVLQ();
        }
        catch {
            return null;
        }
        finally {
            this.#position = pos; // Reset the iterator.
        }
    }
@returns the next VLQ number without iterating further. Or returns null if
the iterator is at the end or it's not a valid number.