🚀 New Release: Configurator Handler Registration

This release introduces a powerful extension point to the configuration system — Configurator.register_handler() — enabling dynamic responses to configuration changes.

✨ New Feature: register_handler

You can now register custom handlers that execute automatically when specific settings are modified.
This is particularly useful for settings that require derived logic or side-effects, such as updating related Matplotlib parameters.

register_handler(name: str, func: Callable[[Any], Dict[str, Any]]) → None

Example (enabled by default):

def _cycle_handler(value):
    # Custom logic to create a cycler object from the value
    return {'axes.prop_cycle': new_cycler}

rc.register_handler('cycle', _cycle_handler)

Each handler function receives the new value of the setting and must return a dictionary mapping valid Matplotlib rc keys to their corresponding values. These updates are applied automatically to the runtime configuration.

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🧩 Why It Matters

This addition:

• Fixes an issue where cycle: entries in ultraplotrc were not properly applied.
• Decouples configuration logic from Matplotlib internals.
• Provides a clean mechanism for extending the configuration system with custom logic — without circular imports or hard-coded dependencies.

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🔧 Internal Improvements

• Refactored configuration update flow to support handler callbacks.
• Simplified rc management by delegating side-effectful updates to registered handlers.

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💡 Developer Note

This API is designed to be extensible. Future handlers may include dynamic color normalization, font synchronization, or interactive theme updates — all powered through the same mechanism.