Support RowsColumnScanner on Go 1.27 - #649

Summary

Go 1.27 applications can retain driver-owned column scanning when a driver is wrapped by otelsql. This lets drivers such as pgx decode PostgreSQL arrays, ranges, and other custom types directly instead of losing that capability at the instrumentation boundary.

The wrapper exposes driver.RowsColumnScanner only when the underlying rows implement it. NextRow continues to emit row events, and non-EOF errors from both NextRow and ScanColumn are recorded on the sql.rows span. ScanColumn errors are returned unchanged to the caller. Earlier Go versions keep the ordinary rows wrapper.

Fixes #557.

Validation

• GitHub CI covers lint, coverage, race, CodeQL, and changelog protection checks.
• Compatibility tests cover Go 1.27, 1.26, and 1.25 across the configured Linux, macOS, and Windows matrix.
• Direct and database/sql integration tests verify ScanColumn error propagation, Error span status, and exception recording.
• PostgreSQL 17 integration passes against pgx PR #2542 at ccd2e56d9941 in all five pgx query modes.
• Wrapped pgx matches direct pgx for bigint[], int4range, and the sql.ConvertAssign boolean fallback.
• Successful wrapped queries emit sql.rows.next without row-span errors.
• A negative control with otelsql v0.43.0 fails to scan bigint[] into []int64, confirming that the integration test detects the missing interface.

New concepts

driver.RowsColumnScanner is an optional Go 1.27 interface that lets a SQL driver advance rows with NextRow and scan each column directly into the caller's destination. database/sql stops calling legacy Rows.Next when this interface is present, so a wrapper must preserve it conditionally rather than implement it for every driver.

This is useful when decoding depends on driver-specific context. pgx can retain its PostgreSQL type map, OID, wire format, and raw bytes instead of first reducing the value to a generic driver.Value.

Post-Deploy Monitoring & Validation

• Search application logs for unsupported Scan, cannot scan, and sql: Scan error after adopting the release.
• Watch the error rate and status of sql.rows spans for Go 1.27 applications.
• Healthy signal: wrapped and unwrapped drivers return identical values, and complex pgx types scan without adapters.
• Failure signal: new scan conversion errors, changed destination values, or elevated sql.rows error spans.
• Mitigation: revert to the previous otelsql release or temporarily use the driver's documented scan adapter.
• Validation window and owner: maintainers during pre-release testing and the first release cycle with Go 1.27.