refactor(ingestion-beam): simplify Decoder pipeline and dedupe log-entry geo lookups

[akkomar]

Follow up to #2857 (comment)

Merging Guidelines

Changes affecting ingestion-edge

Code updates are always safe to merge since production code updates are always
deployed manually.

Changes affecting ingestion-sink

Code updates are always safe to merge since production code updates are always
deployed manually. See these instructions
for updating the code version.

Changes affecting ingestion-beam (including ingestion-core)

• Only merge changes to main that you want to propagate to production automatically
• Check pipeline latency before merging, particularly if:
  • The merge will occur within 2 hours of the UTC date change, or
  • You are merging multiple PRs in quick suggestion

See the full code deployment policy for details.