Add mixed pattern in gcsfs microbenchmarks

[googlyrahman]

The read benchmarks in our microbenchmarks are either (100% sequential 0% seek) or (0% sequential 100% seek) with fixed io size. These are often not correct representation of real world scenarios.

Real world scenarios are mixed of sequential, and seeks with a variable of io size. The following PR add this feature in microbenchmarks to correctly measure the typical real world performance.

Sample output after this PR

| Bucket Type | Group | Pattern | Seq Prob | Files | Folders | Threads | Processes | Depth | Target Type | File Size (MiB) | Chunk Size (MiB) | Min Chunk (MiB) | Max Chunk (MiB) | Block Size (MiB) | Mean Latency (s) | Mean Throughput (MiB/s) | Max CPU (%) | Max Memory (MiB) |
+-------------+-------+---------+----------+-------+---------+---------+-----------+-------+-------------+-----------------+------------------+-----------------+-----------------+------------------+------------------+-------------------------+-------------+------------------+
|   regional  |  read |   seq   |   N/A    |   1   |   N/A   |    1    |     1     |  N/A  |     N/A     |     1024.00     |      16.00       |       N/A       |       N/A       |       5.00       |      30.00       |          143.47         |     0.47    |      224.88      |
|   regional  |  read |  mixed  |   0.3    |   1   |   N/A   |    1    |     1     |  N/A  |     N/A     |     1024.00     |       N/A        |       0.06      |     1024.00     |       5.00       |      30.00       |          328.90         |     1.04    |     2868.44      |
|   regional  |  read |  mixed  |   0.5    |   1   |   N/A   |    1    |     1     |  N/A  |     N/A     |     1024.00     |       N/A        |       0.06      |     1024.00     |       5.00       |      30.00       |          249.38         |     1.14    |     2934.86      |
+-------------+-------+---------+----------+-------+---------+---------+-----------+-------+-------------+-----------------+------------------+-----------------+-----------------+------------------+------------------+-------------------------+-------------+------------------+

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.43%. Comparing base (5596df9) to head (e5386e8).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #822      +/-   ##
==========================================
+ Coverage   79.55%   81.43%   +1.88%     
==========================================
  Files          16       16              
  Lines        3042     3076      +34     
==========================================
+ Hits         2420     2505      +85     
+ Misses        622      571      -51     

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[ankitaluthra1]

Can you please fix the test failure so its ready for merge

[googlyrahman]

Aah this needs to rebased with main to fix the failure, let me do it.