feat(entity): optimize entity save method and add bulk save functionality

[serbanPricop]

• Add commit parameter to Entity.save() method
• Implement save_bulk() method for efficient bulk creation of EAV values
• Modify save() method to collect values and use save_bulk() when commit is True
• Improve performance by reducing database queries during save operations

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• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc.)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

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• Bugfix
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[Dresdn]

Thanks for the PR @serbanPricop! Looking at the use cases for this, I see two use cases I'll keep in mind when adding some comments on the PR. Please do correct me so I can be sure I align with your thoughts! The use cases for this PR I see are:

1. Optimizing saving an Entity with multiple EAV value updates

Looking at test_setting_attributes(), the p.save() current does 4 database operations, 2 per value: 1 get_all_attributes() and another Attribute.save_value(). This would cut it down to 2 operations, regardless the number of attribute updates for an entity!

2. Optimizing saving n Entities with y Attributes using Django's bulk manager methods

Being able to bulk_save() Value objects would be great when trying to bulk save Entity objects.

[Dresdn]

If commit=False, I would expect nothing to be saved to the database, which is line with Django behavior. Instead, what do you think about returning a list[Value] back? This would work for any number of attributes that are updated during an eav.save() call.

[Dresdn]

In line with the other comment, should bulk_save() take a list[Entity]? Or is the use case for this something different than the two scenarios I identified earlier?

Thinking of how Django's bulks_create() works, you pass in a list of objects created in memory that then get written with an optimized database query. In this scenario, I would think that when wanting to update a number of entities, you would do something in your app like:

for patient in patients:
  patient.eav.age = 10
  patient.eav.height = 2.3
  
eav.bulk_save(patients, 10)
Patient.objects.bulk_create(patients)

Note I did a generic eav.bulk_save() as I'm not sure this should be on the Entity manager as inserted into a specific Entity instance versus being on a Model Manager. Maybe that's a future thing, having a manager for a model that has EAV methods on it, but for now, I think a utility function would work just fine too.

Also, thinking about it, we should use the same language as Django with "bulk_update" and their params to not have confusion around things like expecting signals to be called like a typical save()

What do you think?