[BUG] Flat index benchmark shows 0.9999899999999999 recall #1171

cargo run --package diskann-benchmark --release -- run --input-file diskann-benchmark\perf_test_inputs\wikipedia-100K-flat-index.json --output-file ./target/tmp/flat-index-output.json     

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# Running Job 1 of 1 #
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              Data: target/tmp\wikipedia_cohere/wikipedia_base.bin.crop_nb_100000
         Data Type: float32
          Distance: inner_product
           Queries: target/tmp\wikipedia_cohere/wikipedia_query.bin
       Groundtruth: target/tmp\wikipedia_cohere/wikipedia-100K
                 K: 100
           Threads: 4, 8
              Reps: 1

Loading dataset...
  Loaded 100000 vectors of dimension 768
  Queries: 5000, Groundtruth: 5000x100


  K,   Avg cmps,   QPS - mean(max),             Avg Latency,           p99 Latency,               Recall,   Threads
===================================================================================================================
100,     100000,     123.0 (123.0),   32430.0us (32430.0us),   35711.0us (35711us),   0.9999899999999999,         4
100,     100000,     250.4 (250.4),   31909.2us (31909.2us),   33323.0us (33323us),   0.9999899999999999,         8