Delayed foreign allocation

Closes #456

See merge request !716

Better link size estimates

Closes #521

See merge request !712

Do not count the particles in the leaves when looking for the number of foreign particles to allocate.

New ghost iteration scheme

See merge request !714

Updates to the Velociraptor interface for Pascal's runs

See merge request !717

Only write the cooling information to snapshots if we are running with the cooling or temperature policy.

Correclty move the pointer at the top-level when moving from proxy to proxy. Simplify the linking recursion.

Count the number of particles in foregin cells that have tasks only. Allocated memory based on that counter. Link the cells recursively based on that counter.

Modern C approach to memswap after we found issues on ARM architectures with…

See merge request !695

Use a bisection bracketing scheme around the Newton method in the ghost iteration to help with cases where we struggle and oscillate around the correct solution.

Added note about OpenMPI on OP systems

See merge request !713