add advanced sort_by support

[rommelfreddy]

Summary

This PR extends sort_by support in the Content API client so the SDK can represent the full Storyblok sorting syntax
used by the Content Delivery API.

It adds support for:

• single sort definitions via SortBy
• chained comma-separated sorts via SortByCollection
• numeric sort modifiers via :float and :int`
• null handling via :nulls_first and :nulls_last

Storyblok supports richer sort_by expressions than the SDK could previously express. In particular, the actual
implementation could not model:

• chained sorts like name:desc,slug:asc
• numeric modifiers like content.price:asc:float
• null ordering like path:desc:nulls_first

This PR brings the SDK in line with the documented API behavior.

StoriesRequest now accepts:

public SortBy|SortByCollection|null $sortBy = null

This keeps the API compact and breaking-change-free while allowing both simple and advanced sorting scenarios.

What Changed

• SortBy was extended to support:

  • field
  • direction
  • optional dataType
  • optional nulls

• Added new enums:

  • SortByDataType
  • SortByNulls

• Added SortByCollection to represent multiple sort definitions

• Updated StoriesRequest::toArray() so sort_by is generated from either:

  • a single SortBy
  • or a SortByCollection

Examples

Simple default property sorting

new StoriesRequest(
    sortBy: new SortBy('created_at', Direction::Desc),
);

Results into

created_at:desc

Numeric sorting

new StoriesRequest(
    sortBy: new SortBy('content.price', Direction::Asc, SortByDataType::Float),
);
new StoriesRequest(
    sortBy: new SortBy('content.price', Direction::Asc, SortByDataType::Int),
);

Results into

content.price:asc:float
content.price:asc:int

Null handling:

new StoriesRequest(
    sortBy: new SortBy('path', Direction::Desc, null, SortByNulls::First),
);

new StoriesRequest(
    sortBy: new SortBy('path', Direction::Desc, null, SortByNulls::Last),
);

Results into

path:desc:nulls_first
path:desc:nulls_last

Multiple sorts:

new StoriesRequest(
    sortBy: new SortByCollection([
        new SortBy('name', Direction::Desc),
        new SortBy('slug', Direction::Asc),
    ]),
);

Results into

name:desc,slug:asc

Combined advanced sorts

$request = new StoriesRequest(
    sortBy: new SortByCollection([
        new SortBy('first_published_at', Direction::Desc, null, SortByNulls::Last),
        new SortBy('published_at', Direction::Desc, null, SortByNulls::Last),
        new SortBy('created_at', Direction::Desc),
    ]),
);

Results into

first_published_at:desc:nulls_last,published_at:desc:nulls_last,created_at:desc

Tests

Added/updated unit tests for:

• SortBy
• SortByCollection
• StoriesRequest

Verified cases include:

• simple sorting
• advanced sorting with data type modifiers
• null ordering
• chained sorting serialization through StoriesRequest::toArray()

I didn't adjust the existing tests, because the changes are no breaking changes, so all other test still passes.