refactor: replace JSON3 with JSON for deprecation note

[AbrJA]

No description provided.

[Copilot]

Pull request overview

This PR refactors the codebase to replace the JSON3 dependency with JSON.jl for reading/parsing JSON in both the library code and the test suite.

Changes:

• Swap JSON3 usage to JSON.jl (JSON.parse) in type definition loading and fixture/test parsing.
• Update tests to use string-key access patterns consistent with JSON.jl’s parsed objects.
• Update Project.toml dependencies/compat to depend on JSON instead of JSON3.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/type_definitions.jl	Switches type definition JSON parsing from JSON3 to JSON.jl.
test/test_type_definitions.jl	Updates schema/type-definition parsing and expected qualifier extraction to use JSON.jl structures.
test/fixtures.jl	Updates fixture loader to parse with JSON.jl and use string keys throughout.
test/runtests.jl	Replaces using JSON3 with using JSON for the test harness.
Project.toml	Replaces the JSON3 dependency and compat entry with JSON.jl.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[s-celles]

Thanks @AbrJA for this and toon-format/ToonFormat.jl#16
That's very nice.
I'm currently quite busy but will try to address when I will be considering new release for both package.
I think I first need to ensure CI are both triggering and passing when PR are created (it doesn't seems to be the case here ... probably because my .github folder need better settings)