As pointed out by the [bowtie
report](https://bowtie.report/#/dialects/draft4?language=php) there
where some issues when validating the uniqueness of values espec. when
the order of the keys was different.

Add missing breaking change to upgrade guide

Fixes #822

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

This brings the `Constraint` class to PHP 7.2 language level and does
some cleanup along the way.

This pull request introduces a new GitHub Actions workflow for
continuous integration on a 32-bit system. The workflow is configured to
run tests using PHP 8.4 and includes steps for environment setup and
test execution.

### New Continuous Integration Workflow:

*
[`.github/workflows/continuous-integration-32-bit.yml`](diffhunk://#diff-913f89970936b1231274367aff0161dfd9c5ca768783bdf9d1e1961b59aad86eR1-R38):
Added a new workflow named "Continuous Integration" that triggers on
`push` and `pull_request` events targeting the `master` branch. It runs
on `ubuntu-latest` using a 32-bit container
(`shivammathur/node:latest-i386`) and sets up PHP 8.4 with specific
extensions, tools, and configuration before executing tests via
`composer test`.

Fixes #818

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removing outdated comments.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* Removed outdated docblock comments and unnecessary annotations, such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.

This PR will:
- Scan schemas that are being added for `id` properties and register
them if valid schemas
- Avoid altering the `id` for sibling `ref` properties
- Don't register schema or expand refs when found in enum or const

This will fix #827