refactor: Change BaseAuthToken and BaseValidator to abstract

[samsonasik]

Description

Similar to what I proposed on CodeIgniter4 repo, this change class with Base prefix to abstract as never instantiated and only extended at:

• refactor: make BaseService and BaseCollector abstract CodeIgniter4#10531

detected by structarmed:

->rule('base_classes.must_be_abstract', new ExtendedClassMustBeAbstractOrInstantiatedRule('Source', '/^CodeIgniter\\\\Shield\\\\.*Base.*$/'))

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[samsonasik]

Ready for review 👍 Just let me know if it needs to target different branch as it is bc break.

[datamweb]

@samsonasik I consider this change logical and well aligned with object-oriented design principles. Making base classes abstract clearly communicates their intended purpose.They are designed to be extended rather than instantiated directly.

This is also consistent with our existing codebase. For example, we already have BaseModel defined as an abstract class:

abstract class BaseModel extends Model

So, in my opinion, making the other base classes abstract is a natural and consistent continuation of the same design approach already used in Shield.

Although this technically constitutes a breaking change, I don't expect it to affect many users, since these base classes are primarily intended to be extended rather than instantiated directly.

Finally, I would appreciate it if we could consider the feedback from other before merging this change.