Indexing test failure

[cjen1-msft]

https://github.com/microsoft/CCF/actions/runs/18718753284/job/53385821242?pr=7393

The PR's changes should be entirely orthogonal to this failure.

[achamayou]

Previously: #4403, the main change in #6902, slightly obscured by clang-tidy cleanups necessary for the test to build again, is the raising of max_multithread_run_time from 100s to 500s.

[cjen1-msft]

I think this might be something different to #4403? Looks to be failing with a different error message in a different place (but maybe changes to the test would do that).

Also its failing after <5s not 100s or 500s.
(unless there is some thing else here I'm missing)