Only invoke a given cached partial once

Note that this is backed by a LRU cache (which we soon shall see more usage of), so if you're a heavy user of cached partials it may be evicted and
refreshed if needed. But in most cases every partial is only invoked once.

This commit also adds a timeout (the global `timeout` config option) to make infinite recursion in partials
easier to reason about.

```
name              old time/op    new time/op    delta
IncludeCached-10    8.92ms ± 0%    8.48ms ± 1%   -4.87%  (p=0.016 n=4+5)

name              old alloc/op   new alloc/op   delta
IncludeCached-10    6.65MB ± 0%    5.17MB ± 0%  -22.32%  (p=0.002 n=6+6)

name              old allocs/op  new allocs/op  delta
IncludeCached-10      117k ± 0%       71k ± 0%  -39.44%  (p=0.002 n=6+6)
```

Closes #4086
Updates #9588

resources/image.go

@@ -33,6 +33,7 @@ import (
 	color_extractor "github.com/marekm4/color-extractor"
 
 	"github.com/gohugoio/hugo/common/paths"
+	"github.com/gohugoio/hugo/identity"
 
 	"github.com/disintegration/gift"
 
@@ -278,7 +279,7 @@ func (i *imageResource) Filter(filters ...any) (images.ImageResource, error) {
 		gfilters = append(gfilters, images.ToFilters(f)...)
 	}
 
-	conf.Key = helpers.HashString(gfilters)
+	conf.Key = identity.HashString(gfilters)
 	conf.TargetFormat = i.Format
 
 	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
@@ -430,7 +431,7 @@ func (i *imageResource) getImageMetaCacheTargetPath() string {
 	}
 	p1, _ := paths.FileAndExt(df.file)
 	h, _ := i.hash()
-	idStr := helpers.HashString(h, i.size(), imageMetaVersionNumber, cfgHash)
+	idStr := identity.HashString(h, i.size(), imageMetaVersionNumber, cfgHash)
 	p := path.Join(df.dir, fmt.Sprintf("%s_%s.json", p1, idStr))
 	return p
 }