RTEMS | score: Speed up the red-black tree rebalance (!1524)

[Sebastian Huber (@sebhub)]

Sebastian Huber created a merge request: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1524

Project:Branches: sebhub/rtems:up/rbtree-perf to rtems/rtos/rtems:main
Author: Sebastian Huber

## Summary

Issue #5804: Speed up the red-black tree rebalance

The rebalance of the red-black tree loads and stores more than it needs.
The series adds a performance test of the tree, translates the
`bsd-tree.h` macros into static inline functions, flattens the node and
restructures the control flow of the rebalance.  The issue gives the A/B
measurements of eight boards.

The tests `sprbtree01` and `ts-unit-no-clock-0` pass on the boards of all
eight targets, for each of the commits 2 to 4.

## AI Details
<!-- Make sure you have read our statement at https://www.rtems.org/generative-ai/ -->

### Prompt used

None as a single prompt.  The work was done in an interactive Claude Code
session on the RTEMS tree.  The task was to measure the runtime of the
red-black tree, to find the work of the rebalance which it does not need,
and to remove it.  Each change was directed and reviewed.

### AI model used

Claude Opus 5.5 (claude-opus-5-5), through Claude Code.

### How AI was used for the contribution

- ( ) Formatting
- (x) Test creation.
- (x) Code comments.
- ( ) The entire contribution was generated using AI
- ( ) AI code completion such as Copilot in VSCode.

The performance test, the translation of the macros, the implementation
and the A/B measurements were produced in that session under my
direction, and the commit messages were drafted there.

### Access

I have not used a product which claims copyright in its output, and I have
legitimate access to the one I used.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1524
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