feat: Wire V3 snapshot producer to row-lineage state

[laskoviymishka]

this PR closes the missing v3 commit-path wiring for row lineage in iceberg-go (part of #727):
snapshot lineage fields were validated downstream but not fully populated in snapshot producer commit flow.

What changed

v3 snapshot producer now:

• sets snapshot first-row-id from table next-row-id,
• computes snapshot added-rows from manifest-list writer assigned row-id delta (writer.nextRowID - firstRowID),
• keeps v1/v2 flow unchanged.

Added tests for:

• v3 single-commit lineage
• two sequential commits (monotonic, gap-free lineage)
• merge path where assigned delta includes existing rows
• manifest-list writer delta behavior including non-data manifest exclusion

Correctness notes

This aligns with strict lineage advancement in metadata builder (next-row-id += snapshot.added-rows).

Behavior is aligned with Iceberg reference implementations’ commit-time row-lineage model (especially Java writer-delta semantics).