This test was still very GC heavy in Java 8 runs in particular
which seems to slow down request processing to the point of timeouts
in some runs.
This PR completely removes the large number of O(MB) `byte[]` allocations
that were happening in the mock http handler which cuts the allocation rate
by about a factor of 5 in my local testing for the GC heavy `testSnapshotWithLargeSegmentFiles`
run.
Closes#51446Closes#50754