segmenter: fix EcoTaxa import errors

[babo989]

"Fixes two EcoTaxa import blockers reported by Jeremy (issues
fairscope/PlanktoScope3#270, #521):

• `object_contour` exceeds EcoTaxa's 250-char column limit. The polygon emitted in segmenter: emit object_contour polygon for audit visualizer #940 for the audit visualizer is now excluded from
  the TSV. It stays in the per-object metadata.json so the audit visualizer keeps working.
• `Ecotaxa_*` archive/TSV prefix uses a capital E, which EcoTaxa rejects. Lowercased to `ecotaxa_*` in both the zip filename
  (`init.py`) and the TSV filename (`ecotaxa.py`).
• Cleanup of the filename duplication (`Ecotaxa_yotel_4501_yotel_4501_A_004`): the imager's directory layout
  already gives `acq_id = <sample_id>_`, so the redundant prefix is stripped before the ID is concatenated. Now produces
  `ecotaxa_yotel_4501_A_004.zip`.