add multiprocessing

[rvhonorato]

===autogenerated===

This pull request introduces parallel processing to the CLI workflow in src/prodigy_prot/cli.py, allowing multiple structure models to be processed concurrently. The main changes include adding a command-line argument to control processor usage, refactoring the execution logic to use a process pool, and encapsulating model processing in a dedicated function. These updates aim to improve performance and scalability when handling multiple input files or models.

Parallelization and CLI enhancements:

• Added a new command-line argument --number-of-processors (-np) to allow users to specify how many processors to use for parallel execution.
• Refactored the main execution logic to collect tasks and run them in parallel using ProcessPoolExecutor, dynamically adjusting the number of workers based on available tasks.
• Introduced a new process_model function to encapsulate the processing of a single model, capturing and returning its output for sequential printing after parallel execution.

Imports and setup for parallel execution:

• Added imports for ProcessPoolExecutor, as_completed, and StringIO to support parallel processing and output capture.