Crash from cached series ID's referencing mmap'd memory

SeriesIDSet's can contain mmap'd memory from TSI files.

If we keep the SeriesIDSet past the lifetime of the iterator it is associated with, we need to cleanse it of the mmap'd memory, or else we get a segfault.

Corresponding Cloud issue: https://github.com/influxdata/idpe/issues/15900

Start by tracing SeriesIDSet ownership from the TSI iterator and identify where mmap'd memory remains referenced after the iterator ends. Use the corresponding Cloud issue for context, then verify that retaining a SeriesIDSet beyond its iterator lifetime no longer causes a segfault.

Written by the indexing model from the issue text.