fix(vortex-bench): map gs:// scheme to gcs storage label

[brancz]

Rationale for this change

Running the benchmark harness (datafusion-bench / query_bench) against a remote
dataset on Google Cloud Storage (--opt remote-data-dir=gs://…) fails immediately
during benchmark setup with:

Error: unknown URL scheme: gs

vortex-bench's url_scheme_to_storage helper — which maps a data-dir URL scheme to a
storage label used for result reporting — only handled s3 and file, so any gs://
run bailed before a single query executed. S3 remote runs work because s3 is handled;
GCS was simply never covered. make_object_store already supports gs:// for the actual
reads, so the only gap was this reporting helper.

What changes are included in this PR?

• Add a STORAGE_GCS = "gcs" constant.
• Add a "gs" arm to url_scheme_to_storage returning that label.

Verified by running TPC-H SF1 from a GCS bucket end-to-end (DataFusion + Vortex, 22/22
queries executing against gs://…, results tagged storage=gcs).

What APIs are changed? Are there any user-facing changes?

None. This only affects the benchmark harness's storage-label reporting; no public API,
format, or behavior change outside vortex-bench.

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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.

⚡ 2 improved benchmarks
❌ 2 regressed benchmarks
✅ 1591 untouched benchmarks
⏩ 4 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_varbinview_into_canonical[(1000, 10)]	168.9 µs	205.7 µs	-17.87%
❌	Simulation	slice_empty_vortex	339.4 ns	397.8 ns	-14.66%
⚡	Simulation	chunked_varbinview_canonical_into[(100, 100)]	259.5 µs	224.4 µs	+15.64%
⚡	Simulation	chunked_varbinview_into_canonical[(100, 100)]	306.6 µs	271.5 µs	+12.95%

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 polarsignals:fix/vortex-bench-gcs-storage-scheme (e72acdc) with develop (5d3be01)}

Footnotes

1. 4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩