276 use blas

[connoraird]

Description

• Updates the rst nested loop in the kernel to use a BLAS dot product
  • This required refactoring some allocatable arrays into 1d buffers and using pointer arrays to reference them.
• Some additional unused allocatable arrays were also removed

Speedup plot

This plot shows the performance of test test_004_isol_C2H4_4proc_PBE0CRI for 1 mpi process

[connoraird]

The changes in this PR look pretty straightforward to me. It would be interesting to time the loop do nsf3 = 1, ia%nsup with both versions of the code and see how much faster the blas call is. I guess you could do this with one thread so you don't have to worry about the thread-safety of the timers. With the graphs you've shown in the other PRs, I'm not entirely convinced this is making the code significantly faster.

Results of timing nsf3 loop	threads	276-combine-nsf-loops	276-use-blas
1	2.47956 s	1.95329 s
2	1.45973 s	1.24583 s
4	0.77407 s	0.67395 s
8	0.46875 s	0.39146 s
16	0.27807 s	0.22739 s