fix: enforce display condition to return string in render_block filter

[Soare-Robert-Daniel]

Closes #2191

Summary

Because the function render_blocks for block conditions could not return anything, an error is raised because the filter render_block must return a string.

I refactored the function so that it always returns a string. Also, change from add_action to add_filter since render_block exists as a filter, and with the new phpdoc added to the function, phpstan does not allow us to use the add_action since we are always returning something.

Note

By being aware of #2177, in this PR, the introduced test is critical to succeed.

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Test instructions

1. Use Otter Free.
2. Create a new post and insert an Image Block
3. Set the condition to be visible to the Logged User.
4. Check the page if the block is rendered.
5. Log out, then recheck the page. The block should be hidden, and no fatal error should happen.

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Checklist before the final review

• Included E2E or unit tests for the changes in this PR.
• Visual elements are not affected by independent changes.
• It is at least compatible with the minimum WordPress version.
• It loads additional script in frontend only if it is required.
• Does not impact the Core Web Vitals.
• In case of deprecation, old blocks are safely migrated.
• It is usable in Widgets and FSE.
• Copy/Paste is working if the attributes are modified.
• PR is following the best practices

[pirate-bot]

Bundle Size Diff

Package	Old Size	New Size	Diff
Animations	239.1 KB	239.1 KB	0 B (0.00%)
Blocks	1.5 MB	1.5 MB	0 B (0.00%)
CSS	93.17 KB	93.17 KB	0 B (0.00%)
Dashboard	201.53 KB	201.53 KB	0 B (0.00%)
Onboarding	154.18 KB	154.18 KB	0 B (0.00%)
Export Import	90.95 KB	90.95 KB	0 B (0.00%)
Pro	355.91 KB	355.91 KB	0 B (0.00%)

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Plugin build for 33b4b38 is ready 🛎️!

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E2E Tests

Playwright Test Status:

Performance Results

serverResponse: 221.4, firstPaint: 565.3, domContentLoaded: 1578.35, loaded: 1578.85, firstContentfulPaint: 3673.8, firstBlock: 5542.3, type: 12.49, minType: 10.23, maxType: 16.44, typeContainer: 8.25, minTypeContainer: 6.91, maxTypeContainer: 9.43, focus: 42.62, minFocus: 36.91, maxFocus: 53.8, inserterOpen: 27.85, minInserterOpen: 24.37, maxInserterOpen: 32.55, inserterSearch: 6.4, minInserterSearch: 5.98, maxInserterSearch: 7.12, inserterHover: 3.41, minInserterHover: 2.83, maxInserterHover: 4.5, listViewOpen: 158.27, minListViewOpen: 138.7, maxListViewOpen: 204.34

[pirate-bot]

🎉 This PR is included in version 2.6.11 🎉

The release is available on GitHub release

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