Profile Gitaly requests when streaming diffs using DiffBlobs RPC

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In !174863 (comment 2250908739), testing shows that using DiffBlobs RPC when streaming diff files can be slower than when using CommitDiff RPC.

Other than a separate issue regarding collapsed files, @ghinfey noticed that DiffBlobs is ~3x slower even for smaller diffs:

diff_blobs: false, gitaly_duration_s: 0.0770038, db_main_duration_s: 0.0462, duration_s: 0.34266
diff_blobs: true, gitaly_duration_s: 0.2112101, db_main_duration_s: 0.0487, duration_s: 0.473484

@justintobler noted that at the time of this writing (2024-12-19), DiffBlobs is expected to perform worse than CommitDiff (comment). There are some upstream changes to Git being worked on to improve this.

Once we have those changes, we should test and profile again.