This commit adds a GGUF validation check for both the main model file and the `mmproj` file (if present) before they are loaded. This prevents the extension from crashing if an invalid GGUF file is provided.
The `GgufMetadata` interface and `loadMetadata` function were removed as the `readGgufMetadata` is now invoked directly. The code has also been refactored to be more readable, with clearer variable names and more descriptive comments.
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