Add EventTimeFilter and BaseRelation.render_event_time_filtered

[MichelleArk]

Resolves: #294

• Introduces the EventTimeFilter class, which contains properties necessary to render a where filter on a given event time field
• BaseRelation has an optional EventTimeFilter attribute
• BaseRelation.__str__ renders EventTimeFilter, if present to wrap the ref call in a select * from ... where event_time >= lower_bound and event_time < upper_bound
  • if limit also provided, resolve limit first before event-time filter to prioritize performance of input data scans

Postgres testing: https://github.com/dbt-labs/dbt-postgres/actions/runs/10775130606

[github-actions]

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