fix(remove user): handles user removal failures more gracefully

[mvilanova]

No description provided.

[Copilot]

Pull Request Overview

This PR improves error handling for user removal operations in the Slack plugin by gracefully handling cases where users are not found in the Slack workspace. The changes ensure that user removal failures don't cause exceptions and provide better logging and user feedback.

• Enhanced the remove_user method in the Slack plugin with comprehensive error handling for user lookup failures
• Added graceful error handling in case and incident interactive flows when looking up users by email
• Moved try-catch blocks to more appropriate locations in participant removal flows

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/dispatch/plugins/dispatch_slack/plugin.py	Enhanced remove_user method with better error handling, logging, and documentation
src/dispatch/plugins/dispatch_slack/case/interactive.py	Added error handling for user lookup failures in engage and edit functions
src/dispatch/incident/flows.py	Moved try-catch block to wrap the actual remove_user call instead of plugin lookup
src/dispatch/case/flows.py	Moved try-catch block to wrap the actual remove_user call instead of plugin lookup

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