Switch most of our custom algorithms to ranges

[rprospero]

Currently, most of our custom algorithms (e.g. for_each_pair) take a beginning and ending iterator. Now that we have moved to C++20, they can instead take a single object that matches the range concept. This has the opportunity to simplify many of the call sites. For example, in src/kernels/geometry.cpp, the line

dissolve::transform_reduce(ParallelPolicies::par, mol.species()->torsions().begin(), mol.species()->torsions().end(),

could become

dissolve::transform_reduce(ParallelPolicies::par, mol.species()->torsions(),

[trisyoungs]

👍 for this. I was thinking the same thing as I was working through #2195.