Fix Connect.Koi auto-detect throws DateTimeOffset exception when no koi.json exists in default DNN skin

[tvatavuk]

Fixed #17

[Copilot]

Pull request overview

This PR fixes a DateTimeOffset exception that occurs when HostFileChangeMonitor is initialized with a non-existent koi.json file in DNN skins. The fix adds proper file existence checks and fallback cache expiration strategies.

Key Changes:

• Added file existence check before attempting to monitor the koi.json file for changes
• Implemented time-based cache expiration (5 minutes) as a fallback when the file doesn't exist or monitoring fails
• Improved cache key generation by using ToLowerInvariant() instead of ToLower()

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[Copilot]

The cache expiration time of 5 minutes is duplicated on lines 62 and 68. Consider extracting this magic number to a private constant (e.g., CacheFallbackExpirationMinutes) to improve maintainability and make it easier to adjust this value consistently in the future.

[tvatavuk]

@copilot open a new pull request to apply changes based on this feedback

[iJungleboy]

ATM I'm not sure if this is something we want to support, as it doesn't really fix anything.
The correct solution is to get the koi.json and restart.

This method doesn't need the restart, but it will "randomly start working" after the specified time, so I feel like it's not doing much, and could confuse people even further.