ci: add benchmarking via conbench

[kentkwu]

What's Changed

This PR adds a github action workflow to run benchmarks and upload them to conbench.

• https://conbench.arrow-dev.org

Note: Results are only submitted to conbench on push to main. This requires CONBENCH_EMAIL and CONBENCH_PASS to be configured as GitHub Actions secrets

Test Plan

Ran against a locally running conbench container

bash ci/scripts/bench.sh $(pwd) --json

# Transform verification (without submitting):
python3.11 - <<'EOF'
import sys
sys.path.insert(0, '.')
from ci.scripts.bench_adapt import JSAdapter
adapter = JSAdapter(result_fields_override={"info": {}})
results = adapter._transform_results()
print(f"{len(results)} results parsed")
print("First result tags:", results[0].tags)
print("First result stats:", results[0].stats)
EOF

# Local conbench (Docker):
git clone https://github.com/conbench/conbench
cd conbench
# create buildinfo.json (required by the app)
echo '{"commit":"0000000000000000000000000000000000000000","branch_name":"main","build_time_rfc3339":"2026-03-10T00:00:00Z","build_hostname":"localhost","version_string"
:"local"}' > buildinfo.json
docker compose up --build -d
docker compose port app 5000  # get the port
# register at http://127.0.0.1:<port>/register?key=innocent-registration-key

# Full end-to-end submission:
CONBENCH_URL=http://127.0.0.1:<port> \
CONBENCH_EMAIL=<email> \
CONBENCH_PASSWORD=<password> \
CONBENCH_REF=main \
GITHUB_SERVER_URL=https://github.com \
GITHUB_REPOSITORY=apache/arrow-js \
GITHUB_SHA=<commit-sha> \
python3.11 ci/scripts/bench_adapt.py

Viewed runs in conbench UI

Closes #203