feat: reentrant callback group

[sykwer]

Description

TODO

• ThreadConfigurator cannot yet deal with reentrant CallbackGroup parallelism.
• reentrant parallelism is fixed to 4 for now (should be configurable parameter)
• Doc

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Notes for reviewers

[Copilot]

Pull request overview

This PR introduces support for reentrant callback groups in the CallbackIsolatedExecutor, enabling parallel execution of callbacks within the same callback group. The implementation creates a new MultiThreadedExecutorInternal class to handle reentrant callback groups with configurable parallelism (currently hardcoded to 4 threads), while maintaining single-threaded execution for mutually exclusive callback groups.

Changes:

• Added MultiThreadedExecutorInternal class to enable multi-threaded execution for reentrant callback groups
• Modified CallbackIsolatedExecutor to detect and handle reentrant callback groups differently from mutually exclusive ones
• Created a sample ReentrantNode application to demonstrate the reentrant callback group functionality

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
callback_isolated_executor/include/callback_isolated_executor/multi_threaded_executor_internal.hpp	Defines the MultiThreadedExecutorInternal class with thread synchronization primitives for reentrant callback group execution
callback_isolated_executor/src/multi_threaded_executor_internal.cpp	Implements thread pool management, synchronization logic, and executor lifecycle for reentrant callback groups
callback_isolated_executor/include/callback_isolated_executor/callback_isolated_executor.hpp	Adds reentrant parallelism configuration and methods to handle different callback group types
callback_isolated_executor/src/callback_isolated_executor.cpp	Refactors spin logic to route reentrant and mutually exclusive callback groups to appropriate executors
callback_isolated_executor/CMakeLists.txt	Updates build configuration to include new MultiThreadedExecutorInternal implementation
cie_sample_application/include/cie_sample_application/reentrant_node.hpp	Defines ReentrantNode header with reentrant callback group and timer declarations
cie_sample_application/src/reentrant_node.cpp	Implements ReentrantNode with two timers assigned to a reentrant callback group for testing
cie_sample_application/src/reentrant_node_main.cpp	Creates executable entry point for the ReentrantNode sample application
cie_sample_application/CMakeLists.txt	Adds build targets for the new reentrant_node component and executable

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