Add benchmarks and Cargo profile using link-time optimization

[g-bauer]

This PR adds

• A Cargo profile including LTO
• Two groups of benchmarks:
  • dual_numbers provides evaluations of the Helmholtz energy function for different dual number types without constructing a State object.
  • state_properties provides benchmarks for different properties (compressibility, molar_volumes, fugacity coefficient, and isochoric heat capacity for now). The State is constructed within the function that is evaluated for the benchmarks but conditions are given in the natural variables of the Helmholtz energy so that no density iteration has to be conducted.
• A readme for the benchmarks

This PR changes the Cargo profile of the workflow we use to build and publish python wheels to include LTO.

In the future, it might be interesting to also investigate the different contributions for PC-SAFT separately or add additional benchmarks for different pure substances and mixtures.

[prehner]

Exciting update. More performance with only compile times as downside! I have some suggestions to reduce boilerplate in the benchmarks.