Use single regex for meta project id search

What does this MR do and why?

AI Summary

This change optimizes how the search system filters results by project IDs. Previously, when searching across multiple projects, the system would create separate filter conditions for each project ID and combine them with "OR" logic (meaning "show results from project 1 OR project 2 OR project 3").

The new approach combines all project IDs into a single regular expression pattern (like "^1$|^2$|^3$") that matches any of the specified projects in one filter. This simplifies the search query structure and reduces complexity while achieving the same filtering result.

The changes update both the core filtering logic and all the test files to reflect this new, more efficient approach. Instead of generating nested filter structures with multiple conditions, it now generates a single, streamlined filter that's easier to process.

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