Fix: Avoid post__not_in

[dinhtungdu]

Description of the Change

Remove the usage of post__not_in and using php to filter excluded posts instead.

Alternate Designs

n/a

Benefits

See: https://10up.github.io/Engineering-Best-Practices/php/#performance

Possible Drawbacks

There may be a very edge case when

Verification Process

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Closes #3

Changelog Entry

Changed: Remove post__not_in and use php to filter excluded post.

[asharirfan]

Hey @dinhtungdu 👋 I think, I already fixed it in #38 among other phpcs issues.

[dinhtungdu]

@asharirfan yes and ... I'm the one who reviewed it 🤦‍♂️, closing