tidy: Janitorial work for SplineFD

[KSkwarczynski]

Pull request description

Code should be nicer and faster (by small margin...)

Changes or fixes

• vector -> const vector& for speed
• Made templates to more easily clean std::vectors
• Binning wasn't properly deleted
• Find spline segment was making parraler but didn't use for, waste of resources...
• In find spline segment xArray was copied... waste of resources...
• lot of const for const corecctens...
• introduce coeffOffset to avoid multiplciation by 4 so many times...
• SetupSplines wasn't used so removed
• addef fmaf_t to avoid total mess in calcsplinewieght...

Examples

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Memory and CPU Usage Summary

### Memory and CPU Usage Summary

| Metric  |     Mean    |      Max    |
|---------|-------------|-------------|
| **RAM** |   310.04 MB |   313.74 MB |
| **CPU** |    92.40 %  |   118.75 %  |

Memory Usage Plot

• Job Summary Link

You can view the memory usage plot directly in the job summary from the link above.

[EdAtkin]

Thanks for tidying :) makes it all neater.