all: Rework page store, add a dynacache, improve partial rebuilds, and some general spring cleaning

There are some breaking changes in this commit, see gohugoio#11455.

Closes gohugoio#11455
Closes gohugoio#11549

This fixes a set of bugs (see issue list) and it is also paying some technical debt accumulated over the years. We now build with Staticcheck enabled in the CI build.

The performance should be about the same as before for regular sized Hugo sites, but it should perform and scale much better to larger data sets, as objects that uses lots of memory (e.g. rendered Markdown, big JSON files read into maps with transform.Unmarshal etc.) will now get automatically garbage collected if needed. Performance on partial rebuilds when running the server in fast render mode should be the same, but the change detection should be much more accurate.

A list of the notable new features:

* A new dependency tracker that covers (almost) all of Hugo's API and is used to do fine grained partial rebuilds when running the server.
* A new and simpler tree document store which allows fast lookups and prefix-walking in all dimensions (e.g. language) concurrently.
* You can now configure an upper memory limit allowing for much larger data sets and/or running on lower specced PCs.
We have lifted the "no resources in sub folders" restriction for branch bundles (e.g. sections).
Memory Limit
* Hugos will, by default, set aside a quarter of the total system memory, but you can set this via the OS environment variable HUGO_MEMORYLIMIT (in gigabytes). This is backed by a partitioned LRU cache used throughout Hugo. A cache that gets dynamically resized in low memory situations, allowing Go's Garbage Collector to free the memory.

New Dependency Tracker: Hugo has had a rule based coarse grained approach to server rebuilds that has worked mostly pretty well, but there have been some surprises (e.g. stale content). This is now revamped with a new dependency tracker that can quickly calculate the delta given a changed resource (e.g. a content file, template, JS file etc.). This handles transitive relations, e.g. $page -> js.Build -> JS import, or $page1.Content -> render hook -> site.GetPage -> $page2.Title, or $page1.Content -> shortcode -> partial -> site.RegularPages -> $page2.Content -> shortcode ..., and should also handle changes to aggregated values (e.g. site.Lastmod) effectively.

This covers all of Hugo's API with 2 known exceptions (a list that may not be fully exhaustive):

Changes to files loaded with template func os.ReadFile may not be handled correctly. We recommend loading resources with resources.Get
Changes to Hugo objects (e.g. Page) passed in the template context to lang.Translate may not be detected correctly. We recommend having simple i18n templates without too much data context passed in other than simple types such as strings and numbers.
Note that the cachebuster configuration (when A changes then rebuild B) works well with the above, but we recommend that you revise that configuration, as it in most situations should not be needed. One example where it is still needed is with TailwindCSS and using changes to hugo_stats.json to trigger new CSS rebuilds.

Document Store: Previously, a little simplified, we split the document store (where we store pages and resources) in a tree per language. This worked pretty well, but the structure made some operations harder than they needed to be. We have now restructured it into one Radix tree for all languages. Internally the language is considered to be a dimension of that tree, and the tree can be viewed in all dimensions concurrently. This makes some operations re. language simpler (e.g. finding translations is just a slice range), but the idea is that it should also be relatively inexpensive to add more dimensions if needed (e.g. role).

Fixes gohugoio#10169
Fixes gohugoio#10364
Fixes gohugoio#10482
Fixes gohugoio#10630
Fixes gohugoio#10656
Fixes gohugoio#10694
Fixes gohugoio#10918
Fixes gohugoio#11262
Fixes gohugoio#11439
Fixes gohugoio#11453
Fixes gohugoio#11457
Fixes gohugoio#11466
Fixes gohugoio#11540
Fixes gohugoio#11551
Fixes gohugoio#11556
Fixes gohugoio#11654
Fixes gohugoio#11661
Fixes gohugoio#11663
Fixes gohugoio#11664
Fixes gohugoio#11669
Fixes gohugoio#11671
Fixes gohugoio#11807
Fixes gohugoio#11808
Fixes gohugoio#11809
Fixes gohugoio#11815
Fixes gohugoio#11840
Fixes gohugoio#11853
Fixes gohugoio#11860
Fixes gohugoio#11883
Fixes gohugoio#11904
Fixes gohugoio#7388
Fixes gohugoio#7425
Fixes gohugoio#7436
Fixes gohugoio#7544
Fixes gohugoio#7882
Fixes gohugoio#7960
Fixes gohugoio#8255
Fixes gohugoio#8307
Fixes gohugoio#8863
Fixes gohugoio#8927
Fixes gohugoio#9192
Fixes gohugoio#9324

Author: bep

.github/workflows/test.yml

@@ -87,6 +87,12 @@ jobs:
         curl -LJO "https://github.com/sass/dart-sass/releases/download/${env:SASS_VERSION}/dart-sass-${env:SASS_VERSION}-windows-x64.zip";
         Expand-Archive -Path "dart-sass-${env:SASS_VERSION}-windows-x64.zip" -DestinationPath .;
         echo  "$env:GITHUB_WORKSPACE/dart-sass/" | Out-File -FilePath $Env:GITHUB_PATH -Encoding utf-8 -Append
+    - if: matrix.os == 'ubuntu-latest'
+      name: Install staticcheck
+      run: go install honnef.co/go/tools/cmd/staticcheck@latest
+    - if: matrix.os == 'ubuntu-latest'
+      name: Run staticcheck
+      run: staticcheck ./...
     - if: matrix.os != 'windows-latest'
       name: Check
       run: |