Small performance improvements

[juliasloan25]

Minor issues found in #390 that we want to clean up for better performance.

Tasks

Beta Give feedback

1. don't pass FT as an argument
2. wrap pi in FT for calculations
3. use zero(FT) instead of FT(0) to reduce allocations
4. remove use of parent (except where needed when spaces aren't identical ?)
5. make sure no closures over global variables (e.g. FT
6. limit use of Val to only when necessary

some points taken from #323