constructor() {
        this.operationCount = 0;
        this.body = "";
        const tempGuid = coreUtil.randomUUID();
        // batch_{batchid}
        this.boundary = `batch_${tempGuid}`;
        // --batch_{batchid}
        // Content-Type: application/http
        // Content-Transfer-Encoding: binary
        this.subRequestPrefix = `--${this.boundary}${HTTP_LINE_ENDING}${HeaderConstants.CONTENT_TYPE}: application/http${HTTP_LINE_ENDING}${HeaderConstants.CONTENT_TRANSFER_ENCODING}: binary`;
        // multipart/mixed; boundary=batch_{batchid}
        this.multipartContentType = `multipart/mixed; boundary=${this.boundary}`;
        // --batch_{batchid}--
        this.batchRequestEnding = `--${this.boundary}--`;
        this.subRequests = new Map();
    }
Inner batch request class which is responsible for assembling and serializing sub requests.
See https://learn.microsoft.com/en-us/rest/api/storageservices/blob-batch#request-body for how requests are assembled.