[d0w]

Summary

Modifies the client.TCP listener to accept connections concurrently rather than synchronously. This allows multiple connections to be accepted at once while avoiding hanging connections and setups from preventing new connections from being made. The change also adds a timeout for connection setups only so that they do not have to be manually closed.

Related Issue

Closes #4512

Changes

• Moves the Tunnel or Forward step when setting up a new connection to a sandbox or ssh client into a separate goroutine outside of the listener loop.
• Connection setups now have a 30 second timeout period after which the tunnel is automatically closed. This is done by using a separate context that is cancelled via a timer.
• Adds tests to assert that concurrent connections do not block each other and that hanging connections are closed after a timeout.

Release Notes

Testing

• Checks appropriate to the affected code and behavior pass
• Unit tests added/updated (if applicable)
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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