Extend custom Processor API

[C-Achard]

Scope

Introduces improved custom processors in the GUI, especially focusing on how processor instances are created, configured, notified of recording events, and cleaned up.
Adds support for passing detailed recording context to processors, allows processors to opt into being built in the worker process, and improves logging and error handling throughout the lifecycle.

This gives the processors far broader capabilities:

• Can operate on context passed from the GUI, e.g. recording file paths
• Can execute custom logic specifically on recording start/stop
• May be constructed the same way as the 1.0 version of live-GUI for legacy compat
• Adds much better logging re: custom processor creation and operation

TODO:

• Reset DLC_LIFECYCLE_EXTRA_LOGS to False in config.py.

Automated summary

Processor lifecycle and context management:

• Adds hooks in main_window.py to notify processors when recording starts and stops, passing a detailed context dictionary, and provides a generic method to save processor data on stop (_notify_processor_recording_started, _notify_processor_recording_stopped, _save_processor_data_if_available, _build_processor_recording_context) [1] [2].
• Updates BaseProcessorSocket to support context-aware saving, including new methods for setting/getting recording context and save paths, and implements on_recording_started and on_recording_stopped hooks [1] [2].
• The processor save() method now uses the context-provided path if available and logs more informative messages.

Processor instantiation and configuration:

• Introduces ProcessorSpec dataclass to represent processor construction parameters, and utilities to create specs and determine if a processor should be built in the worker (create_spec_from_scan, processor_builds_in_worker) [1] [2].
• Modifies processor instantiation logic in main_window.py to use specs for worker-built processors and to log context at key points.
• Updates dlc_processor.py to support configuration with either a processor instance or a spec, to track which was used, and to clean up processor instances on reset/shutdown [1] [2] [3] [4].

Logging and debugging improvements:

• Adds a new DLC_LIFECYCLE_EXTRA_LOGS config flag and a log_processor_context utility to emit detailed lifecycle logs for debugging processor handling [1] [2].
• Enables extra logging around processor instantiation, worker startup, and cleanup [1] [2].

Processor API enhancements:

• BaseProcessorSocket gains the experimental PROCESSOR_BUILD_IN_WORKER attribute to signal where it should be constructed.
• The stop() method in BaseProcessorSocket now optionally saves data before stopping.

These changes together make the processor workflow more robust, flexible, and debuggable, especially for advanced/experimental processor plugins and custom user extensions.