feat(si): add specific power quantity

[swaits]

Specific power is used to represent a power-to-weight ratio, like in vehicles or human power; as in watts per kilogram or ft-lbf/s per pound.

Added the SpecificPower quantity using the existing Power quantity as a guideline.

For more information on this quantity, please see a description of specific power on Wikipedia.

[iliekturtles]

Thanks for the PR! I still need to do a more in depth review, and have started test actions in the meantime.

Some of the units have multiple divisions (e.g. erg per second per kilogram). Are these commonly used this way? I've only skimmed the referenced article at this point, but generally multiple divisions avoided: https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-6-rules-and-style-conventions-printing-and-using#616

[swaits]

I really only know of specific power's use in W/kg, (ft-lbf/<unit time>)/lb, and hp/lb. I'm completely aligned with deleting things like (erg/s)/kg as I only included it because I started with power.rs as my baseline (i.e. it's copypasta). If we're wrong and someone needs it in the future, they can ask for it or submit their own PR.

[swaits]

Oh... that said, I felt it important to include this one...

// Less commonly used, but more accurate (reduced) derived unit of specific power.
@square_meter_per_cubic_second: 1.0_E0; "m² · s⁻³", "square meter per cubic second", "square meters per cubic second";

... because that's the true base unit, even though it's not as commonly used as multiplied by kg/kg to look like W/kg.

[swaits]

Please LMK if there's anything else I can do to help make this one acceptable for merge. And thank you for considering it!

[iliekturtles]

Could rebase and resolve the si/mod.rs conflight? Otherwise I just need to finish my review. #370 is up next, then this this PR.

[iliekturtles]

I reviewed and pushed a commit to your fork. Please review, rebase, and squash the commits!

• Formatting for readability.
• Fix conversion factor used for pounds.
• Check all units based on the units they are derived from.
  • Add check_units_energy test.

[swaits]

Hey, yes, I'll try to get to this today... I'm pretty buried in $DAYJOB but excited to figure this one out.