Investigate slow performance with python 3.14

[danielhollas]

Benchmark results show significant slow downs. See 2.8.0rc1-py3.14 and 2.8.0rc1-py3.12. Need to investigate it before we merge it. For now we decided to mention Python 3.14 support only in the CHANGELOG, because there is no Beta marker for python support.

Originally posted by @agoscinski in #7263 (comment)

[danielhollas]

Notably, the upcoming python 3.14.5 (to be released next week) will revert the new incremental GC that shipped in 3.24

It is possible that the slowness seen in #7263 had been due to GC (perhaps unlikely, the revert was not due to performance but due to increased memory) so probably worth testing again once 3.14.5 is released.