Fix custom classnames rule with VueJS objects within list syntax.

Description

This PR fixes an issue occurring with the no-custom-classname rule, where it did not detect custom classes inside object in list patterns:
<div :class="[{'custom-not-detected': true}]"/>.

Fixes #319

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Breaking change => existing will work, but more warnings will be issued

How Has This Been Tested?

New tests have been added. They're all using vue-eslint-parser in a .vue file.

• Testing for invalid/valid classes when using object within list
• Testing with a mix of valid/invalid within the object, and with classes written directly in the array.
• Testing with multiple objects and classes between them, in an array.

Test Configuration:

• OS + version: macOS Sequoia 15.0 (24A335)
• NPM version: 10.8.3
• Node version: 22.6.0

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas => should probably comment in ast as it's an important part of the plugin?
• I have made corresponding changes to the documentation => no need as it's a fix
• My changes generate no new warnings => it probably will as it can detect new classes
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

• VSCode with TS automatically removed some unreachable code.
• I added a check in the ast util, it's working well as all tests passed, but I don't know if it is the cleanest way to do that.