Implement metrics evaluators that work directly with ContentStats

[anoopj]

Feature Request / Improvement

Problem

Followup from PR feedback.

The content file adapters convert ContentStats to v3 style bounds. Each call allocates a new map and, for bounds serializes every field value into a fresh ByteBuffer.

This is acceptable when a single evaluator calls each method once per file, but if multiple evaluators are used (e.g. InclusiveMetricsEvaluator + StrictMetricsEvaluator), the maps are rebuilt and discarded repeatedly.

Fix

Add metrics evaluators that work directly with ContentStats / FieldStats rather than going through the ContentFile bounds/counts maps. This avoids the intermediate map allocation and per-field serialization.

Once ContentStats-aware evaluators are available, ensure they are used in all v4 code paths (scan planning, manifest filtering, etc.) instead of falling back to the adapter's map-based methods.

Query engine

None

Willingness to contribute

• I can contribute this improvement/feature independently
• I would be willing to contribute this improvement/feature with guidance from the Iceberg community
• I cannot contribute this improvement/feature at this time

[anoopj]

Working on this.