Potential Dangling Pointers in `createTree` Function

As discussed in [PR #3729](https://github.com/acts-project/acts/pull/3729#discussion_r1829372523), there is a potential issue with storing addresses of loop variables in the `createTree` function, which could lead to dangling pointers if `spacePoints` gets modified or goes out of scope. Addressing this issue would involve major changes in several parts of the ACTS project and is out of scope for PR #3729. This issue is opened to track the work required to resolve this in a future PR.\n\nRequester: @CarloVarni