Use the stream_call method when using the Gitaly Client for querying Diff Stats
What does this MR do?
Related to #209786 (closed) and #30334 (closed)
While investigating in this MR !33037 (merged), there were some inconsistencies between what our different profiling tools outputted. In the performance bar, it was showing Gitaly having a very low time when we were on a merge request #diffs page, for either the metadata or batches call.
See: 
However, other profiling tools were showing that the Gitaly time for these two were very high. Switching to the Gitaly client streaming_call method fixes this and shows the correct time taken:
See: 
I have tracked performance between the two, and there were no noticeable differences.
Screenshots
Does this MR meet the acceptance criteria?
Conformity
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Changelog entry -
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Availability and Testing
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Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process. -
Tested in all supported browsers -
Informed Infrastructure department of a default or new setting change, if applicable per definition of done
Security
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Label as security and @ mention @gitlab-com/gl-security/appsec -
The MR includes necessary changes to maintain consistency between UI, API, email, or other methods -
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