Fixes sub-task #308: folder clearing paths

[hanna-meda]

Description

Fixes #308
Adds directory existence/emptiness checks and two new Self-host Google Fonts scenarios to verify cache folders cleanup when toggling Self-host GF with RUCSS on/off.

Type of change

• 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).
• Sub-task of GF: As a QA, I'd like the css/fonts data clearing scenarios to be automated #187
• Chore
• Release

Detailed scenario

What was tested

Ran npm run test:test for the newly added scenarios under self-host-google-fonts.feature:

• Scenario: Should clear cache and used CSS when toggling Self-host GF with RUCSS on
• Scenario: Should clear cache/used CSS/fonts CSS with RUCSS off/on while toggling Self-host GF

Test results screenshot:

How to test

Add @test to the two new scenarios in src/features/self-host-google-fonts.feature, then run npm run test:test.
Or run the whole feature with npm run test:selfhostgooglefonts (no tags needed).

Technical description

Documentation

E2E coverage was updated with two new self-host GF scenarios and added folder existence/emptiness checks

New dependencies

N/A

Risks

List possible performance & security issues or risks, and explain how they have been mitigated.

Mandatory Checklist

Code validation

• I validated all the Acceptance Criteria. If possible, provide screenshots 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.

Code style

• I wrote a self-explanatory code about what it does.
• I protected entry points against unexpected inputs.
• I did not introduce unnecessary complexity.
• Output messages (errors, notices, logs) are explicit enough for users to understand the issue and are actionnable.

Unticked items justification

N/A

Additional Checks

• In the case of complex code, I wrote comments to explain it.
• When possible, I prepared ways to observe the implemented system (logs, data, etc.).
• I added error handling logic when using functions that could throw errors (HTTP/API request, filesystem, etc.)