Add a dormant v4 RDS Postgres dual-write to the CI benchmark emitters

[connortsui20]

The CI benchmark emitters currently need a manual vortex-bench-migrate run to populate the new v4 RDS Postgres database. This adds a best-effort, env-gated dual-write so the emitters populate it directly: a new --postgres mode in scripts/post-ingest.py (IAM auth, verify-full TLS, a five-table-plus-commit upsert keyed on measurement_id, NaN/Inf guard, best-effort site revalidate), plus scripts/_measurement_id.py, a byte-for-byte port of the Rust measurement_id hash so re-ingests upsert the existing row instead of duplicating. The existing v2 and v3 write paths are untouched, and the v3 --server path stays stdlib-only.

It ships dormant: the v4 step added to bench.yml, sql-benchmarks.yml, and v3-commit-metadata.yml is gated on vars.GH_BENCH_INGEST_ROLE_ARN and carries continue-on-error: true, so with the variable unset the new code is dead-but-safe and a v4 failure can never fail a workflow. Provisioning the IAM role and setting that variable is a separate ops step after this merges.

The measurement_id port is verified against the cross-language golden vectors (65 pass); those vectors and the parity test live in vortex-data/benchmarks-website with the Rust source of truth rather than in this repo, and the heavier testcontainer and revalidate checks are run out-of-band.

🤖 Generated with Claude Code

Note from human (connor): This is the only thing that needs to be merged on this repo. Everything else after that needs to be done outside of this repo. That's really just configuring AWS (Vortex account), vercel project, migration of the old data, and repo secrets / variables.

[codspeed-hq]

Merging this PR will degrade performance by 14.56%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 1 improved benchmark
❌ 7 regressed benchmarks
✅ 1573 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	decompress_rd[f64, (10000, 0.01)]	108.9 µs	139.3 µs	-21.82%
❌	Simulation	decompress_rd[f64, (10000, 0.1)]	109.2 µs	139.6 µs	-21.79%
❌	Simulation	decompress_rd[f64, (10000, 0.0)]	108.9 µs	139.2 µs	-21.77%
❌	Simulation	decompress_rd[f32, (100000, 0.0)]	496.1 µs	583.9 µs	-15.04%
❌	Simulation	decompress_rd[f32, (10000, 0.1)]	78.2 µs	91.4 µs	-14.4%
❌	Simulation	decompress_rd[f32, (10000, 0.01)]	78.2 µs	91.1 µs	-14.16%
❌	Simulation	decompress_rd[f32, (10000, 0.0)]	78.7 µs	91.3 µs	-13.88%
⚡	Simulation	eq_i64_constant	317.9 µs	287.9 µs	+10.42%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing ct/bench-v4-emitter-dual-write (aa5a15a) with develop (9814173)}