Use precalculated zoekt counts when available

What does this MR do and why?

Use precalculated zoekt counts when available. This is a continuation of gitlab-zoekt-indexer!638 (merged).

AI Summary

This change updates the Zoekt search engine version from 1.3.2 to 1.4.1 and modifies how search result counts are handled. The code now prioritizes using more direct count values (FileMatchCount and LineMatchCount) when they're available in the search response, falling back to the previous counting method only when these direct counts aren't present. This improves the accuracy and efficiency of reporting how many files and lines match a search query. Tests were also added to verify that these new count fields work correctly when provided by the search engine.

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