Add encrypt/decrypt throughput benchmarks

[clintfred]

As an ironoxide user
I want to understand the encrypt/decrypt performance of the library

We have latency benchmarks for encrypt and decrypt, but not throughput ones. Some work was done on this on https://github.com/IronCoreLabs/ironoxide/tree/92-throughput but that branch is somewhat old now. It was not merged because we wanted to build the throughput benches around the async API, which did not exist at that time.

AC

• Unmanged encrypt throughput bench - operations/second
• Encrypt throughput bench - operations/second
• Unmanaged decrypt throughput bench - operations/second
• Decrypt throughput bench - operations/second
• (probably need this) a way to configure the tests to only process a certain number of requests per second (semaphore has been suggested for impl, but should think about this from first principles again)