RUST-1473 Add GridFS Benchmarks

[isabelatkinson]

benchmark patch: https://spruce.mongodb.com/version/636ae9b9306615468cacbff2/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

[patrickfreed]

Code changes all look good to me, but from looking at the patch link, it doesn't seem like the GridFS benchmarks are actually being run. Is this patch out of date? e.g. https://evergreen.mongodb.com/task_log_raw/mongo_rust_driver_benchmarking_driver_benchmarks__async_runtime~tokio_auth_and_tls~auth_and_tls_os~ubuntu_18.04_benchmark_4.2_replica_set_patch_1037712e4fb060c406e3f0cdeeaa0fdbcb762b84_636ae9b9306615468cacbff2_22_11_08_23_44_00/0?type=T#L1130

Also, it looks like GridFsDownloadStream needs to be publicly exported at the gridfs module level, though that's not strictly related to this PR.

[isabelatkinson]

new patch: https://spruce.mongodb.com/version/6373fe0ed6d80a307003bef9/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

Also, it looks like GridFsDownloadStream needs to be publicly exported at the gridfs module level, though that's not strictly related to this PR.

this is fixed in the upload stream PR

[patrickfreed]

Code changes LGTM!

I compared the results of our benchmark to the Node driver's, and it does seem like we're a bit slower in GridFS:

• Download: 304 MB/s (Rust) vs 564 MB/s (Node)
• Upload: 162 MB/s (Rust) vs 371 MB/s (Node)

Unfortunately, the Node driver doesn't seem to have results for the parallel GridFS benchmarks, so not sure how we compare there.

For the Download one, it looks like the difference might be down to us buffering the whole 50MB file in memory. It's possible we could improve this by pre-allocating the vec that we're downloading to. We could also have a dummy AsyncWrite implementation that just discards the bytes, but that seemed not in the spirit of the benchmark (I tried this and did see much faster numbers, btw).

I honestly can't tell why the Upload shows such a stark difference, especially given that Rust way outperforms Node in the LargeDocInsertOne benchmark. I think we should file a ticket and look into it in the future if GridFS performance is ever deemed an issue by users.

Here's the Node driver patch I used as a reference: https://evergreen.mongodb.com/task/mongo_node_driver_next_performance_tests_run_spec_benchmark_tests_8254575d7a33539c7e7e5cb0e3b621f49a7336e3_22_11_16_20_41_05

[kmahar]

one nit but LGTM besides that, don't need to re-review

[kmahar]

nit: could we mention what n is in the docstring?

[abr-egn]

LGTM!