Metal quantized modifications proposal.

- Add a device param, wherever needed.
- Create new QMetal storage thing that implements QuantizedType.
- Update everywhere needed.

Fix Python.

Fixing examples.

Fix: fmt + clippy + stub.

Moving everything around.

Only missing the actual implems.

Fixing everything + adding dequantized kernels.

More work.

Fixing matmul.

Fmt + Clippy

Some clippy fixes.

Working state.

Q2K Metal -> Bugged (also present in GGML).
Q4K CPU -> Bugged (present previously, new test catch it).
Q5K CPU -> Bugged (present previously).
Q8_1 Both -> Never really implemented it seems
Q8K metal -> Never implemented in metal

Fixing Q2K bug (present in ggml).

candle-examples/examples/quantized-t5/main.rs

@@ -132,7 +132,8 @@ impl T5ModelBuilder {
     }
 
     pub fn build_model(&self) -> Result<t5::T5ForConditionalGeneration> {
-        let vb = t5::VarBuilder::from_gguf(&self.weights_filename)?;
+        let device = Device::Cpu;
+        let vb = t5::VarBuilder::from_gguf(&self.weights_filename, &device)?;
         Ok(t5::T5ForConditionalGeneration::load(vb, &self.config)?)
     }