Cap the default backend worker count

[harsh21234i]

Summary

• Cap the automatically selected Redis-backed backend worker count at 8.
• Preserve the Granian-specific GRANIAN_WORKERS override.
• Clarify worker configuration in deployment docs and add unit coverage for CPU-count boundaries.

Closes #7541

Testing

At commit 2dc6659:

• uv run pytest tests/units/utils/test_processes.py -q (36 passed)
• Applicable pre-commit hooks passed.

The documentation wording was subsequently clarified in commit adf3a98; please rerun pre-commit on the current head.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no blocking issues were found.

Summary

Cap the automatically selected Redis-backed backend worker count at eight.

• Redis-backed backends now cap their automatic worker count at eight.

_{Reviews (3) · Last reviewed commit: "Update docs/hosting/self-hosting.md" · Reviewed by Greptile}

[codspeed]

Merging this PR will not alter performance

⚠️ 12 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• test_get_state[disk]
• test_cli_startup[version]
• test_cli_startup[help]
• test_import_cli
• test_cli_startup[run_help]
• test_cli_startup[cloud_help]
• test_cli_startup[deploy_help]
• test_set_state[disk]
• test_get_state[memory]
• test_modify_state[disk]
• …and 2 more

✅ 148 untouched benchmarks

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_{Comparing harsh21234i:fix/7541-cap-backend-workers (993cd1c) with main (2eb1b44)}

[cubic-dev-ai]

All reported issues were addressed across 7 files

<sub>Reply with feedback, questions, or to request a fix.

View guided diff | Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 7 files

<sub>Reply with feedback, questions, or to request a fix.

View guided diff | Re-trigger cubic</sub>

[masenf]

thanks