tcpproxy: Refactor, fix bugs and potential panics

[denpeshkov]

This PR refactors tcpproxy package and fixes some bugs and panics:

• Use atomic.Bool for remote.inactive instead of a mutex to improve performance and reduce struct size
• Use zap's no-op logger when none is provided by the client, removing repeated nil checks
• Preallocate slices
• Replace for loops with range loops
• Use strconv.Itoa for int-to-string conversion instead of fmt.Sprintf for better performance
• Use uint64 for pickCount to avoid overflow issues
• Create the timer once and reset it on each loop iteration to avoid allocating a new timer every time
• Add timeout for dialing
• Simplify serve logic
• Protect donec with a mutex
• Add checks in Stop to prevent panic when stopping before Run or closing an already closed channel

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: denpeshkov
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[k8s-ci-robot]

Hi @denpeshkov. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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