fix(core): bound WAL-backed rollout pagination memory

[beinan]

Summary

• page source=all and source=wal through an id-only LSM scan so wide claim-check columns never enter the full LSM sort
• locate selected ids in each physical base/WAL dataset using only id and _rowid, then fetch exactly the page rows with take_rows
• preserve global filter, offset, ordering, has_more, schema-evolution alignment, and inline-blob projection behavior
• add regression coverage for mixed base/WAL pagination, deep-page completion, filters, wide text values, and WAL-only reads

Testing

• ./.codex/skills/ci-pr-helper/scripts/run_ci_checks.sh
• 216 core/workspace Rust tests passed, 3 ignored; integration, master, and server tests passed
• 213 Python tests passed, 6 skipped, 3 xfailed
• cargo fmt, cargo clippy, ruff format/check, and pyright passed
• all GitHub Actions checks passed