[GGUF] metadata serialization into Uint8Arrray (#1740)

### Description 

This PR introduces function that serializes GGUF metadata/header into
Uint8Arrray so that I can use
#1718 to update gguf
metadata on hf.co

* `serializeTypedMetadata()` - Serialize GGUF metadata to binary format
* `serializeGgufHeader()` - Create complete GGUF headers with metadata +
tensor info + alignment
* Enhanced `gguf()` function - Now returns `littleEndian` property for
endianness detection

### Usage example

```ts
// Edit first kB of file
await commit({
  repo,
  accessToken: "hf_...",
  operations: [{
    type: "edit",
    originalContent: new Blob(original gguf header),
    edits: [{
      start: 0,
      end: 1000,
      content: new Blob(serializeGgufHeader(new gguf header with updated metadata))
    }]
  }]
})
```

Author: mishig25