feat: incremental gguf parser (#10822)

* incremental gguf parser
* gguf: update test to not rely on gguf on disc
* re-use existing create gguf
* read capabilities from gguf kv
* kv exists
* update tests
* s/doneFunc/successFunc/g
* new buffered reader

---------

Co-authored-by: Bruce MacDonald <brucewmacdonald@gmail.com>

fs/gguf/lazy.go

@@ -0,0 +1,89 @@
+package gguf
+
+import (
+	"encoding/binary"
+	"iter"
+	"log/slog"
+)
+
+type lazy[T any] struct {
+	count  uint64
+	next   func() (T, bool)
+	stop   func()
+	values []T
+
+	// successFunc is called when all values have been successfully read.
+	successFunc func() error
+}
+
+func newLazy[T any](f *File, fn func() (T, error)) (*lazy[T], error) {
+	it := lazy[T]{}
+	if err := binary.Read(f.reader, binary.LittleEndian, &it.count); err != nil {
+		return nil, err
+	}
+
+	it.values = make([]T, 0)
+	it.next, it.stop = iter.Pull(func(yield func(T) bool) {
+		for i := range it.count {
+			t, err := fn()
+			if err != nil {
+				slog.Error("error reading tensor", "index", i, "error", err)
+				return
+			}
+
+			it.values = append(it.values, t)
+			if !yield(t) {
+				break
+			}
+		}
+
+		if it.successFunc != nil {
+			it.successFunc()
+		}
+	})
+
+	return &it, nil
+}
+
+func (g *lazy[T]) Values() iter.Seq[T] {
+	return func(yield func(T) bool) {
+		for _, v := range g.All() {
+			if !yield(v) {
+				break
+			}
+		}
+	}
+}
+
+func (g *lazy[T]) All() iter.Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i := range int(g.count) {
+			if i < len(g.values) {
+				if !yield(i, g.values[i]) {
+					break
+				}
+			} else {
+				t, ok := g.next()
+				if !ok {
+					break
+				}
+
+				if !yield(i, t) {
+					break
+				}
+			}
+		}
+	}
+}
+
+func (g *lazy[T]) rest() (collected bool) {
+	for {
+		_, ok := g.next()
+		collected = collected || ok
+		if !ok {
+			break
+		}
+	}
+
+	return collected
+}