Add experimental MLX backend and engine with imagegen support (#13648)

* WIP - MLX backend with gemma3

* MLX: add cmake and go tag build toggles

To build the new MLX backend code:
  cmake --preset MLX
  cmake --build --preset MLX --parallel
  cmake --install build --component MLX
  go build -tags mlx .

Note: the main.go entrypoint for the MLX engine will change in a follow up commit.

* add experimental image generation runtime

* add experimental image generation runtime

* MLX: wire up cuda build for linux

* MLX: get dependencies correct and dedup

This is still too large for a unified github artifact, but is now "correct" for the mlx_cuda_v13
directory.

* fix relative link bug in dedup

* Add darwin build and readme

* add go build tag for mlx dependent code and wire up build_darwin.sh

* lint cleanup

* macos: build mlx for x86

This will be CPU only.

* cuda build instructions and fix drift from mlx bump

* stale comment

* Delete agent helper doc

* Clean up readme.md

* Revise README for tokenizer clarity and details

Updated README to clarify tokenizer functionality and removed correctness section.

---------

Co-authored-by: jmorganca <jmorganca@gmail.com>

x/ml/nn/convolution.go

@@ -0,0 +1,30 @@
+package nn
+
+import "github.com/ollama/ollama/x/ml"
+
+type Conv2D struct {
+	Weight ml.Tensor `gguf:"weight"`
+	Bias   ml.Tensor `gguf:"bias"`
+}
+
+func (m *Conv2D) Forward(ctx ml.Context, t ml.Tensor, s0, s1, p0, p1, d0, d1 int) ml.Tensor {
+	t = m.Weight.Conv2D(ctx, t, s0, s1, p0, p1, d0, d1, 1)
+	if m.Bias != nil {
+		// Bias shape is (out_channels,) while t shape is (width, height, out_channels, batch)
+		t = t.Add(ctx, m.Bias.Reshape(ctx, 1, 1, -1))
+	}
+	return t
+}
+
+type Conv3D struct {
+	Weight ml.Tensor `gguf:"weight"`
+	Bias   ml.Tensor `gguf:"bias"`
+}
+
+func (m *Conv3D) Forward(ctx ml.Context, t ml.Tensor, s0, s1, s2, p0, p1, p2, d0, d1, d2, g int) ml.Tensor {
+	t = m.Weight.Conv3D(ctx, t, s0, s1, s2, p0, p1, p2, d0, d1, d2, g)
+	if m.Bias != nil {
+		t = t.Add(ctx, m.Bias)
+	}
+	return t
+}