[DOP-28871] Use bulk DB fetch in consumer

[dolfinus]

Change Summary

Change consumer DB rows fetching pattern from:

for item in items:
  existing = await db.get(item)
  if not existing:
    existing = await.db.create(item)

To:

existing_list = await db.get_bulk(items)
for item in items:
  if item not in existing_list:
    await db.create(item)

This is done in new DatabaseSaver class which replaces save_to_db function.

Before - 760RPS, 10.04% on save_to_db() + 5.28% on SQLAlchemy query cache = 15.32% of al traces.

After - 860RPS, 3.51% on DatabaseSaver.save() + 1.02% on SQLAlchemy query cache = 3.53% of all traces.

Related issue number

Checklist

• Commit message and PR title is comprehensive
• Keep the change as small as possible
• Unit and integration tests for the changes exist
• Tests pass on CI and coverage does not decrease
• Documentation reflects the changes where applicable
• docs/changelog/next_release/<pull request or issue id>.<change type>.rst file added describing change
  (see CONTRIBUTING.rst for details.)
• My PR is ready to review.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
data_rentgen/consumer
saver.py	128	13	89%	37–38, 140–146, 148–149, 152–153
data_rentgen/db/repositories
column_lineage.py	58	7	87%	65, 74, 87, 96, 106, 124, 142
job.py	67	3	95%	121, 143–144
location.py	69	1	98%	141
run.py	92	31	66%	123–125, 133–136, 139–143, 147–149, 152–155, 158–159, 162, 177–179, 187, 204–206, 208–209
user.py	29	2	93%	42–43
data_rentgen/db/scripts/seed
__main__.py	60	4	93%	78–79, 84–85
TOTAL	6964	398	94%