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/main.rs

@@ -9,7 +9,7 @@ use std::io::Write;
 use tokenizers::Tokenizer;
 
 use candle::quantized::{ggml_file, gguf_file};
-use candle::{Device, Tensor};
+use candle::Tensor;
 use candle_transformers::generation::LogitsProcessor;
 
 use candle_examples::token_output_stream::TokenOutputStream;
@@ -361,6 +361,7 @@ fn main() -> anyhow::Result<()> {
     let model_path = args.model()?;
     let mut file = std::fs::File::open(&model_path)?;
     let start = std::time::Instant::now();
+    let device = candle_examples::device(false)?;
 
     let mut model = match model_path.extension().and_then(|v| v.to_str()) {
         Some("gguf") => {
@@ -377,10 +378,11 @@ fn main() -> anyhow::Result<()> {
                 &format_size(total_size_in_bytes),
                 start.elapsed().as_secs_f32(),
             );
-            ModelWeights::from_gguf(model, &mut file)?
+            ModelWeights::from_gguf(model, &mut file, &device)?
         }
         Some("ggml" | "bin") | Some(_) | None => {
-            let model = ggml_file::Content::read(&mut file).map_err(|e| e.with_path(model_path))?;
+            let model = ggml_file::Content::read(&mut file, &device)
+                .map_err(|e| e.with_path(model_path))?;
             let mut total_size_in_bytes = 0;
             for (_, tensor) in model.tensors.iter() {
                 let elem_count = tensor.shape().elem_count();
@@ -486,7 +488,7 @@ fn main() -> anyhow::Result<()> {
 
         let start_prompt_processing = std::time::Instant::now();
         let mut next_token = {
-            let input = Tensor::new(prompt_tokens.as_slice(), &Device::Cpu)?.unsqueeze(0)?;
+            let input = Tensor::new(prompt_tokens.as_slice(), &device)?.unsqueeze(0)?;
             let logits = model.forward(&input, 0)?;
             let logits = logits.squeeze(0)?;
             logits_processor.sample(&logits)?
@@ -507,7 +509,7 @@ fn main() -> anyhow::Result<()> {
         let start_post_prompt = std::time::Instant::now();
         let mut sampled = 0;
         for index in 0..to_sample {
-            let input = Tensor::new(&[next_token], &Device::Cpu)?.unsqueeze(0)?;
+            let input = Tensor::new(&[next_token], &device)?.unsqueeze(0)?;
             let logits = model.forward(&input, prompt_tokens.len() + index)?;
             let logits = logits.squeeze(0)?;
             let logits = if args.repeat_penalty == 1. {