Closes #7058: Implement DJE Safe Mode Feature

[Miraeld]

Description

Fixes #7058
This change introduces the "Delay JavaScript Execution safe mode" feature. It enhances user control over JavaScript execution, providing a checkbox to enable or disable safe mode, and displays a warning about potential performance impacts. This helps users manage their site's performance more effectively.

Type of change

• Enhancement (non-breaking change which improves an existing functionality).

Detailed scenario

To trigger the new code:

• Navigate to the plugin settings.
• Locate the "Delay JavaScript Execution" section.
• Check the "Delay JavaScript Execution safe mode" checkbox.
• Observe the warning message detailing potential performance impacts.
• Default exclusion will be added on the front-end.

Technical description

Documentation

The feature adds a checkbox labeled "Delay JavaScript Execution safe mode" and displays a warning when it is checked. The backend logic updates the exclusions list based on the checkbox state and ensures these changes are applied when settings are saved.
Also, when we load delay_js on the front-end, we check if the new option is enabled, and if this is the case, we add default exclusion to delay_js.

New dependencies

No new dependencies are introduced in this change.

Risks

None.

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.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 1a097421	❌ 38.78% (target: 50.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (1a09742)	Report Missing	Report Missing	Report Missing
Head commit (d37773c)	38145	16704	43.79%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#7081)	49	19	38.78%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

1. Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct. ↩

[Miraeld]

Codacy Diff Coverage is failing due to the addition of a field on the front-end which isn't triggered in any test (as it's front-end). That's normal 👍