Adding benchmarks

[josediegorobles]

We use rust for security about all, but for speed too, so would be a good idea to add benchmarking framework to the repository and the CI

[crisdut]

I will start some tests about that, but this does not happen after RGB Watcher because we can create PSBT with a tweak now. If tests works, I will close this PR.

[cryptoquick]

I think a good benchmark would be to mint as many assets are needed to make the stock 32MB in size. This number is chosen because the maximum any single contract can be is 16MB, but stock can hold multiple contracts, so it's good to know how long it takes to get to that size.

This would also serve to give us a better idea of the limits of the RGB stock; it'd suck if strict encoding had some issues that weren't obvious until it was used to encode large amounts of data.

Also, we should use conditional compilation to set Carbonado to use c0 format for the benchmark instead of c15, that way we're not testing the speed of Carbonado formats. Let me know if you need any help with that.