redirect cleanup: cleanup plugins and tunnels

[bneradt]

This adds more cleanup logic to redirect handling logic, cleaning up the tunnel and PluginVCs on redirect. This addresses a timeout crash we received on dispatch to a defunct plugin upon following a redirect from the escalate plugin.

[Copilot]

Pull Request Overview

This PR adds comprehensive cleanup logic to the redirect handling path in the HttpSM to prevent timeout crashes when following redirects from plugins. The fix addresses a specific crash scenario where a defunct plugin would receive dispatch events after a redirect from the escalate plugin.

• Adds tunnel cleanup to kill active tunnels before redirect processing
• Implements transform and plugin agent cleanup when hooks are set
• Ensures plugin tunnels are properly terminated and nullified

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[bneradt]

Making this a draft because I want to bake this in Yahoo prod for longer to make sure this patch is stable.