Fix comparing unstable metadata

While testing reduction outputs with exdf-compare, I noticed that the test for metadata and/or timestamps occassionally fail:

• The metadata test fails due to EXtra-data iterating over files and returning the first result, which often will deliver files with different sequence number and thus failing on sequenceNumber
• Timestamps sometimes differ between aggregators, causing the test to fail with an output generated with exdf-reduce's INDEX conflict resolution

exdf-compare therefore now ignores METADATA/sequenceNumber and allows for a 1ms difference between timestamps. exdf-reduce also no longer prints a warning if INDEX root data if the timestamps are within that range.

@kluyvert You may have been aware of this already, but FYI.