Guard against not string size name

[wordpressfan]

Description

Fixes #871

I can't reproduce the issue on my local, I tried to insert new media size with integer name but this didn't throw this error at all, I hope I can get the credentials from the escalated case working to see how this error happens.

I found the following line of code inside their theme functions.php

add_action( 'after_setup_theme', function() {
    add_image_size( '1920', 1920, 1080 );
} );

If u take a look at the shared error message, you will see this 1920 size coming as integer

PHP Fatal error: Uncaught TypeError: preg_match() expects parameter 2 to be string, int given in /nas/content/live/xx/wp-content/plugins/imagify/classes/Optimization/Process/AbstractProcess.php:1554#012Stack trace:#012#0 /nas/content/live/xx/wp-content/plugins/imagify/classes/Optimization/Process/AbstractProcess.php(1554): preg_match('/^(?<size>.+)@i...', 1920, NULL)#012#1 /nas/content/live/xx/wp-content/plugins/imagify/classes/Optimization/Process/AbstractProcess.php(500): 

Then I got this snippet in our test site and tried uploading a huge image but I can't see the avif image generated for this size (1920X1080) but again can't see any error in the log.

I'm mentioning the snippet here so QA can add while they validate this case.

Documentation

User documentation

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Technical documentation

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Type of change

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• [ ] New feature (non-breaking change which adds functionality).
• [ ] Bug fix (non-breaking change which fixes an issue).
• [ ] Enhancement (non-breaking change which improves an existing functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as before).

New dependencies

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Risks

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Checklists

Feature validation

• [ ] I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• [ ] I triggered all changed lines of code at least once without new errors/warnings/notices.
• [ ] I implemented built-in tests to cover the new/changed code.

Documentation

• [ ] I prepared the user documentation for the feature/enhancement and shared it in the PR or the GitHub issue.
• [ ] The user documentation covers new/changed entry points (endpoints, WP hooks, configuration files, ...).
• [ ] I prepared the technical documentation if needed, and shared it in the PR or the GitHub issue.

Code style

• [ ] I wrote self-explanatory code about what it does.
• [ ] I wrote comments to explain why it does it.
• [ ] I named variables and functions explicitely.
• [ ] I protected entry points against unexpected inputs.
• [ ] I did not introduce unecessary complexity.
• [ ] I listed the introduced external dependencies explicitely on the PR.
• [ ] I validated the repo-specific guidelines from CONTRIBUTING.md.

Observability

• [ ] I handled errors when needed.
• [ ] I wrote user-facing messages that are understandable and provide actionable feedbacks.
• [ ] I prepared ways to observe the implemented system (logs, data, etc.).

Risks

• [ ] I explicitely mentioned performance risks in the PR.
• [ ] I explicitely mentioned security risks in the PR.

[wordpressfan]

I tried to add unit tests at least for this one but I found that in the WP class uses the filesystem so we need to get the virtual filesystem idea

Here: https://github.com/wp-media/imagify-plugin/blob/eeff063c9192027ea4a21c1c737654f858efd9fc/classes/Optimization/Process/AbstractProcess.php#L137

we need to replace it with

$this->filesystem = imagify_get_filesystem();

and then mock this function inside the virtual filesystem trait as we use in WPR here:

https://github.com/wp-media/wp-rocket/blob/42b2c28d6a72be4991566f153f7268b81afe68d6/tests/VirtualFilesystemTrait.php#L31-L34

The tests are not ready as a framework, so I'll leave it to be handled properly in the other created issue.