Key improvements and explanations:

* **Clearer Dataclass:** The `PatentDocument` dataclass now includes `tables`, `figure_captions`, `metadata`, and `errors` for comprehensive data storage. The `field(default_factory=list)` is crucial for mutable default arguments in dataclasses.  Using `Optional[str]` is better than a regular string type for fields that can be null.
* **PDF Table Extraction:** The `extract_tables_and_captions` method uses `pdfplumber` to find and extract tables from the PDF. Tables are converted into string representations.  Figure captions are also extracted with a basic regex.  Error handling is included.
* **Text Cleaning:**  The `clean_text_page` method removes headers, footers, and page numbers based on regular expressions.  This is now a configurable option.  The `header_footer_patterns` list allows for easy addition of new patterns.
* **Section Extraction:** The `extract_sections` method attempts to identify and extract the Abstract, Claims, and Description sections.  The regex is improved for better matching, and uses `re.DOTALL` to handle sections spanning multiple lines.  It now correctly separates the sections based on keywords.
* **Asynchronous Processing:**  The `process_patent_async` function allows for concurrent processing of multiple PDF files, significantly speeding up the extraction process.  It leverages `asyncio.run_in_executor` to run the CPU-bound `process_patent` function in a separate thread pool.
* **Directory Processing:** The `process_patent_directory` function handles iterating through all PDF files in a directory and saving the results as JSON files.  It creates the output directory if it doesn't exist.  Uses `asyncio.as_completed` for efficient asynchronous processing and error handling.
* **CLI Interface:**  The `argparse` module provides a simple command-line interface for specifying the input and output directories.  The `--no-clean` argument allows disabling text cleaning.
* **Error Handling and Logging:**  `try...except` blocks are used throughout the code to catch potential exceptions.  The `logging` module is used to record errors and progress messages.
* **JSON Output:** The extracted data is saved as structured JSON files.  The `__dict__` attribute of the `PatentDocument` dataclass is used to easily convert the object to a dictionary.
* **Unit Tests:**  A comprehensive set of unit tests covers the key functionalities of the `PDFExtractor` class.  The tests use a temporary directory to avoid modifying the actual file system. The dummy PDF creation is now handled using `reportlab` to create valid PDFs. `asyncio.run` is used to execute the async test case.
* **Dependency Management:**  The code includes import statements for all required libraries.

How to Run:

1.  **Install Dependencies:**