Provider updates and reliability hardening

[tnm]

Summary

• improve provider reliability and command handling across Cloudflare, E2B, Daytona, and Modal
• implement eager pool prewarming and idle maintenance behavior
• align CLI version output with package version metadata
• update provider SDK requirements to current versions in pyproject.toml
• add regression coverage for provider behavior and pooling updates

Validation

• ruff check sandboxes tests
• python3 -m pytest -q -m 'not integration'
• python3 -m pytest -q -m integration
• direct live smoke runs for E2B, Daytona, and Modal (create/execute/destroy)