[chore] bump go structr cache version -> v0.6.0 (#2773)

* update go-structr library -> v0.6.0, add necessary wrapping types + code changes to support these changes

* update readme with go-structr package changes

* improved wrapping of the SliceCache type

* add code comments for the cache wrapper types

* remove test.out 😇

---------

Co-authored-by: tobi <31960611+tsmethurst@users.noreply.github.com>

vendor/codeberg.org/gruf/go-structr/key.go

@@ -0,0 +1,58 @@
+package structr
+
+import (
+	"sync"
+
+	"codeberg.org/gruf/go-byteutil"
+)
+
+// Key represents one key to
+// lookup (potentially) stored
+// entries in an Index.
+type Key struct {
+	raw []any
+	key string
+}
+
+// Key returns the underlying cache key string.
+// NOTE: this will not be log output friendly.
+func (k Key) Key() string {
+	return k.key
+}
+
+// Equal returns whether keys are equal.
+func (k Key) Equal(o Key) bool {
+	return k.key == o.key
+}
+
+// Value returns the raw slice of
+// values that comprise this Key.
+func (k Key) Values() []any {
+	return k.raw
+}
+
+// Zero indicates a zero value key.
+func (k Key) Zero() bool {
+	return k.raw == nil
+}
+
+var buf_pool sync.Pool
+
+// new_buffer returns a new initialized byte buffer.
+func new_buffer() *byteutil.Buffer {
+	v := buf_pool.Get()
+	if v == nil {
+		buf := new(byteutil.Buffer)
+		buf.B = make([]byte, 0, 512)
+		v = buf
+	}
+	return v.(*byteutil.Buffer)
+}
+
+// free_buffer releases the byte buffer.
+func free_buffer(buf *byteutil.Buffer) {
+	if cap(buf.B) > int(^uint16(0)) {
+		return // drop large bufs
+	}
+	buf_pool.Put(buf)
+}