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

helpers/general.go

@@ -23,7 +23,6 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
-	"strconv"
 	"strings"
 	"sync"
 	"unicode"
@@ -31,8 +30,6 @@ import (
 
 	"github.com/gohugoio/hugo/common/loggers"
 
-	"github.com/mitchellh/hashstructure"
-
 	"github.com/gohugoio/hugo/common/hugo"
 
 	"github.com/spf13/afero"
@@ -219,7 +216,7 @@ func ReaderContains(r io.Reader, subslice []byte) bool {
 // GetTitleFunc returns a func that can be used to transform a string to
 // title case.
 //
-// The supported styles are
+// # The supported styles are
 //
 // - "Go" (strings.Title)
 // - "AP" (see https://www.apstylebook.com/)
@@ -523,20 +520,3 @@ func PrintFs(fs afero.Fs, path string, w io.Writer) {
 		return nil
 	})
 }
-
-// HashString returns a hash from the given elements.
-// It will panic if the hash cannot be calculated.
-func HashString(elements ...any) string {
-	var o any
-	if len(elements) == 1 {
-		o = elements[0]
-	} else {
-		o = elements
-	}
-
-	hash, err := hashstructure.Hash(o, nil)
-	if err != nil {
-		panic(err)
-	}
-	return strconv.FormatUint(hash, 10)
-}