This pull request includes several changes to improve the metrics management system and update the alt text reminder functionality. The most important changes include adding user ID hashing, modifying the metrics manager to handle existing data, and updating the alt text check queue to use a different identifier.

Metrics Management Improvements:

• metrics.go: Added SHA-256 hashing for user IDs to enhance privacy. This includes a new hashUserID function and modifications to the MetricEvent struct to store hashed user IDs. [1] [2] [3]
• metrics.go: Implemented the loadAndHashExistingData function to load existing data and ensure all user IDs are hashed. This function is called during the initialization of the MetricsManager.
• metrics.go: Modified the saveToFile method to include an optional locking mechanism to ensure thread safety.
• metrics.go: Moved the run method to the end of the file and reintroduced it with necessary changes to call saveToFile with locking.

Alt Text Reminder Update:

• main.go: Changed the queuePostForAltTextCheck function to use replyPost.Account.ID instead of replyPost.Account.Acct for queuing alt text checks.