SNOW-1805174 Enable single buffer by default

[sfc-gh-mbobowski]

Overview

SNOW-1805174

This PR contains:

• enabling single buffer by default + fixes for some tests
• validation that blocks running iceberg ingestion with double buffer

Pre-review checklist

• [ ] This change should be part of a Behavior Change Release. See go/behavior-change.
• [ ] This change has passed Merge gate tests
• [ ] Snowpipe Changes
• [ ] Snowpipe Streaming Changes
• [ ] This change is TEST-ONLY
• [ ] This change is README/Javadocs only
• [ ] This change is protected by a config parameter eg snowflake.ingestion.method.
  • [ ] Yes - Added end to end and Unit Tests.
  • [ ] No - Suggest why it is not param protected
• [ ] Is his change protected by parameter on the server side?
  • [ ] The parameter/feature is not yet active in production (partial rollout or PrPr, see Changes for Unreleased Features and Fixes).
  • [ ] If there is an issue, it can be safely mitigated by turning the parameter off. This is also verified by a test (See go/ppp).

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