This pull request refactors the `BaseConstraint` class in the
`JsonSchema` package to improve code readability, enforce immutability,
and align with modern PHP practices. The changes include replacing
anonymous functions with static closures, updating type casting, and
removing outdated comments.

### Code modernization and immutability:

* Replaced anonymous functions with `static` closures in methods like
`addError`, `addErrors`, and `convertJsonPointerIntoPropertyPath` to
enforce immutability and improve performance.
[[1]](diffhunk://#diff-05cd63f6b003f185a215e10402525e33d94466ec4d83a685c5a6ccd1befcf921L53-R48)
[[2]](diffhunk://#diff-05cd63f6b003f185a215e10402525e33d94466ec4d83a685c5a6ccd1befcf921L81-R75)
[[3]](diffhunk://#diff-05cd63f6b003f185a215e10402525e33d94466ec4d83a685c5a6ccd1befcf921L167-R162)
* Updated type casting for better readability and adherence to modern
PHP conventions, e.g., `(string)` instead of `strval`.

### Code readability and cleanup:

* Removed outdated docblock comments and unnecessary annotations, such
as the `@return` tag in `convertJsonPointerIntoPropertyPath`.
* Replaced `\JSON_ERROR_NONE` with the `JSON_ERROR_NONE` constant for
consistency with the `use` statement.

### Other improvements:

* Adjusted the `json_decode` call to explicitly set the `associative`
parameter to `false` for clarity.