feat: Pre-populate version.content cache when getting version object

[fsbraun]

Description

The checks framework triggers database hits when accessing a version.content object. This PR adds the content object to the version's field cache to avoid these unnecessary database hits.

The failing test against django-cms@develop-4 fails due to an import order issue for the core's cms.toolbar.toolbar.CMSToolbar. This prevents the core to use versioning's prefetching and is fixed by django-cms/django-cms#8120

Related resources

• feat: Optimize DB queries for edit and structure endpoints django-cms#8120
• #...

Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

Summary by Sourcery

Enhancements:

• Improve performance by reducing database hits when accessing version content.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request pre-populates the version's field cache with the content object when retrieving a version, avoiding database hits when accessing the version's content.

Sequence diagram for optimized version content retrieval

sequenceDiagram
    participant Client
    participant Version
    participant Database

    Client->>Version: get_for_content(content_object)
    Version->>Database: Query version by content_object.pk
    Database-->>Version: Return version
    Note over Version: Cache content_object in version._state.fields_cache
    Note over Version: Cache version in content_object._version_cache
    Version-->>Client: Return version with cached content

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Class diagram showing Version model caching changes

classDiagram
    class Version {
        -_state: ModelState
        +get_for_content(content_object)
        +convert_to_proxy()
        +content: ContentObject
    }

    class ModelState {
        -fields_cache: dict
    }

    class ContentObject {
        -_version_cache: Version
    }

    Version *-- ModelState
    Version -- ContentObject

    note for Version "Added caching of content object
in fields_cache to avoid DB hits"

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File-Level Changes

Change	Details	Files
Pre-populate the version's field cache with the content object.	Added version._state.fields_cache['content'] = content_object to the get_for_content method.	djangocms_versioning/models.py
Preserve the field cache when converting a version to a proxy.	Store the field cache before deep copying the version object. Restore the field cache after deep copying the version object.	djangocms_versioning/models.py

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[sourcery-ai]

Hey @fsbraun - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

---

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[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.77%. Comparing base (f68190c) to head (0417e3a).

Files with missing lines	Patch %	Lines
djangocms_versioning/cms_config.py	75.00%	0 Missing and 1 partial ⚠️
djangocms_versioning/cms_toolbars.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #446      +/-   ##
==========================================
- Coverage   90.63%   89.77%   -0.87%     
==========================================
  Files          72       72              
  Lines        2702     2718      +16     
  Branches      314      318       +4     
==========================================
- Hits         2449     2440       -9     
- Misses        179      201      +22     
- Partials       74       77       +3     

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