Fix Form Marketing List ID fetch and improve error handling

[Soare-Robert-Daniel]

Closes #1835

Summary

ℹ️ From the last Form update, the internal structure was slightly modified. The relaxed type hint from PHPDocs made the problem invisible to PHPStan.

🔩 The type hint is now more strict.
🐛 Improved error display in Editor.
🔧 Test Provider feature has been simplified.

Screenshots

Showcase the working API and error display.

2023-08-30.11-26-37.mp4

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Test instructions

⚠️ You will need a Mailchimp and Sendinblue API Key.

1. Insert a Form.
2. Go to marketing integration and use valid API Keys to check the functionality.
3. Try to use an invalid key format (like a random string) to see if errors appear as notices in the bottom-left corner.

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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	270.81 KB	270.81 KB	0 B (0.00%)
Blocks	1.42 MB	1.42 MB	132 B (0.01%)
CSS	85.28 KB	85.28 KB	0 B (0.00%)
Dashboard	122.49 KB	122.49 KB	0 B (0.00%)
Export Import	83.17 KB	83.17 KB	0 B (0.00%)
Pro	303.34 KB	303.34 KB	0 B (0.00%)

[pirate-bot]

Plugin build for 89f423a is ready 🛎️!

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[pirate-bot]

E2E Summary

Typing

Test	Average Time (ms)	Standard Deviation (ms)	Median Time (ms)	Quantile for soft limit (%)	Quantile for hard limit (%)
Typing	52.88	3.46	51.41	100 (60ms)	100 (80ms)

Values above 60ms

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[irinelenache]

@Soare-Robert-Daniel Tested and the issue is fixed now 🚀
Found some other problem:

• When i'm using the Test service feature, i'm getting an error even if it works and the otter-form email is added to the contact list. (The behaviour is the same for Sendinblue and Mailchimp)

[irinelenache]

@Soare-Robert-Daniel Checked again and everything's fine now ✔️

[pirate-bot]

🎉 This PR is included in version 2.4.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀