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

3 files changed, 41 insertions, 3 deletions

diff --git a/hugolib/page_test.go b/hugolib/page_test.go
index 1d9e3e348..939d06d41 100644
--- a/hugolib/page_test.go
+++ b/hugolib/page_test.go
@@ -24,6 +24,7 @@ import (
 
 	"github.com/bep/clock"
 	"github.com/gohugoio/hugo/htesting"
+	"github.com/gohugoio/hugo/identity"
 	"github.com/gohugoio/hugo/markup/asciidocext"
 	"github.com/gohugoio/hugo/markup/rst"
 	"github.com/gohugoio/hugo/tpl"
@@ -2001,3 +2002,37 @@ Page1: {{ $p1.Path }}
 
 	b.AssertFileContent("public/index.html", "Lang: no", filepath.FromSlash("Page1: a/B/C/Page1.md"))
 }
+
+func TestPageHashString(t *testing.T) {
+	files := `
+-- config.toml --
+baseURL = "https://example.org"
+[languages]
+[languages.en]
+weight = 1
+title = "English"
+[languages.no]
+weight = 2
+title = "Norsk"
+-- content/p1.md --
+---
+title: "p1"
+---
+-- content/p2.md --
+---
+title: "p2"
+---
+`
+
+	b := NewIntegrationTestBuilder(IntegrationTestConfig{
+		T:           t,
+		TxtarString: files,
+	}).Build()
+
+	p1 := b.H.Sites[0].RegularPages()[0]
+	p2 := b.H.Sites[0].RegularPages()[1]
+	sites := p1.Sites()
+
+	b.Assert(identity.HashString(p1), qt.Not(qt.Equals), identity.HashString(p2))
+	b.Assert(identity.HashString(sites[0]), qt.Not(qt.Equals), identity.HashString(sites[1]))
+}
diff --git a/hugolib/resource_chain_test.go b/hugolib/resource_chain_test.go
index 4edc2cb31..6249c0aad 100644
--- a/hugolib/resource_chain_test.go
+++ b/hugolib/resource_chain_test.go
@@ -26,11 +26,10 @@ import (
 	"testing"
 	"time"
 
-	"github.com/gohugoio/hugo/helpers"
-
 	qt "github.com/frankban/quicktest"
 
 	"github.com/gohugoio/hugo/common/loggers"
+	"github.com/gohugoio/hugo/identity"
 	"github.com/gohugoio/hugo/resources/resource_transformers/tocss/scss"
 )
 
@@ -122,7 +121,7 @@ FAILED REMOTE ERROR DETAILS CONTENT: |failed to fetch remote resource: Internal
 |StatusCode: 500|ContentLength: 16|ContentType: text/plain; charset=utf-8|
 
 
-`, helpers.HashString(ts.URL+"/sunset.jpg", map[string]any{})))
+`, identity.HashString(ts.URL+"/sunset.jpg", map[string]any{})))
 
 		b.AssertFileContent("public/styles.min.a1df58687c3c9cc38bf26532f7b4b2f2c2b0315dcde212376959995c04f11fef.css", "body{background-color:#add8e6}")
 		b.AssertFileContent("public//styles2.min.1cfc52986836405d37f9998a63fd6dd8608e8c410e5e3db1daaa30f78bc273ba.css", "body{background-color:orange}")
diff --git a/hugolib/site.go b/hugolib/site.go
index 2ffc3a346..0ca7a81b4 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -778,6 +778,10 @@ func (s *SiteInfo) DisqusShortname() string {
 	return s.Config().Services.Disqus.Shortname
 }
 
+func (s *SiteInfo) GetIdentity() identity.Identity {
+	return identity.KeyValueIdentity{Key: "site", Value: s.language.Lang}
+}
+
 // SiteSocial is a place to put social details on a site level. These are the
 // standard keys that themes will expect to have available, but can be
 // expanded to any others on a per site basis