Adopt spaniter v0.1.0 row iterator adapters

[apstndb]

Summary

• update github.com/apstndb/spaniter from v0.1.0-alpha.1 to v0.1.0
• use spaniter row-iterator lifecycle helpers for metadata/stats capture
• preserve eager PROFILE stats when --redact-rows drains rows without materializing them
• document that redacted eager result sets may have nil rows while still preserving metadata and stats

Validation

• go test ./...
• make test
• git diff --check

[gemini-code-assist]

Code Review

This pull request integrates the github.com/apstndb/spaniter library to handle Spanner row iterator draining and sequencing, replacing custom iterator helpers in main.go and integration_test.go. It also introduces BuildResultSetFromParts in jqresult/protojson.go to support constructing result sets with redacted rows while preserving metadata and query stats, and adds a corresponding integration test. There are no review comments, so I have no feedback to provide.

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