Add ABI marker to RegisteredThreadInfo structure

[Katze719]

• Introduced an ABI marker in the RegisteredThreadInfo struct to intentionally change its layout, indicating a major version bump.

[Copilot]

Pull Request Overview

This PR introduces an ABI marker to the RegisteredThreadInfo structure to intentionally change its memory layout, signaling a major version bump in the library's binary interface. The changes also include build system updates to handle runtime ABI compatibility testing with old and new versions of the ThreadSchedule library.

Key changes:

• Build configuration updated to use headers from old ThreadSchedule installation while linking against current runtime
• Code formatting improvement in thread affinity logic (return statement restructured)

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
integration_tests/runtime_abi_compat/libB/CMakeLists.txt	Refactored build configuration to separate header inclusion from linking, enabling ABI compatibility testing between versions
include/threadschedule/thread_wrapper.hpp	Reformatted conditional return statement for better readability

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