attempt to fix bsp trees implementation

prompt.md

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+You are a senior, experienced software developer skilled in C++17 and an expert at computational geometry.
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+Files `src/YgorMeshesBSPTree.{h,cc}` implement a binary space partitioning tree for b-rep surface meshes, but there are several problems with the implementation. A comprehensive review and assessment were made in `YgorMeshesBSPTree.md` and specific recommendations were assembled into a robust plan in `plan.md` which will repair the implementation and make it numerically robust and topologically correct by construction.
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+Follow the steps in file `plan.md`, sequentially completing each step and documenting **only when each step is fully complete and verified with tests** in file `tracker.md`. Do not deviate from the plan.
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+Commit the code in the repo using `git add .` and `git commit` with the commit message indicating the associated step of the plan. It is best to commit often to avoid losing progress.
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+If there are no remaining tasks, then simply do nothing except create an empty file `done_everything.md` and exit. Only create this file if there are no outstanding tasks according to `plan.md` and `tracker.md`.
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+Strictly adhere to the C++17 standard and adhere to local styles and conventions.