Add Benchmarks

[mitchmindtree]

It would be extremely useful to have a series of benchmarks for testing and demonstrating the feasibility of the sample crate for users.

Benchmarks that would be nice to have:

• All sample format conversions.
• Sample rate conversion speed for a large buffer of frames for each Interpolator.
• Signal generators - sine, square, saw, noise, noise_walk - test varying frame sizes (mono, stereo, 6x, etc).
• Adding and multiplying signals.

We should compare the performance of each task to other rust audio libraries that offer similar functionality. It would also be useful to add one or two well-known C/C++ libraries for comparison, though this might significantly complicate setup.