ENG-2736 - Remove Sandbox Unresponsive

[DamianB-BitFlipper]

The way that the prime cli handles "unresponsive" is not accurate. It is simply a timeout. Remove the concept of "unresponsive", and treat it as a timeout. If unresponsive sandboxes are an issue, the way to detect them would be with a liveliness checks and heartbeats.

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Note

Simplifies sandbox timeout handling and removes the "unresponsive" concept.

• Removes SandboxUnresponsiveError (and its exports) and maps gateway timeouts to CommandTimeoutError in both sync/async execute_command
• Adds a small client timeout buffer (effective_timeout + 2s) to prevent premature client-side timeouts
• Bumps prime-sandboxes to 0.2.12
• Minor CLI/utilities cleanup (logging/messages/formatting) in RL commands and env utils; no functional changes

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