external ingest: fix bloom filters when synthetic prefix is used

[RaduBerinde]

We found that we do not un-apply the synthetic prefix when checking bloom filters. The result is that SeekPrefixGE will more often than not miss keys. This is a major bug that affects Online Restore and is causing corruption on tpcc tests.

I investigated why the metamorphic test did not find this issue. I found that a objDB map wasn't updated properly which lead to the code generating SeekPrefixGE operations not being able to use the keys that were written.

In addition to fixing the bug, I am identifying some key testing misses that got us here:

• the metamorphic test code is a bit lax in testing its assumptions; for example, we should have asserted when objDB returned a 0 value
• there aren't enough tests for the metamorphic generation code
• there is a tendency to over-rely on the metamorphic tests; in this instance we were missing test coverage for SeekPrefixGE in the context of synthetic prefixes