feat: add computational work and computational perf units

[dssgabriel]

This PR adds support for computational work (FLOP) and computational performance (FLOP per second) units.

This lets us do, e.g., the following calculations:

$ cpc '10 zflop / 100 pflop per second'
1.15740740740740740740740740740740740741 days

$ cpc '7 * 1024 * 2048 * 128 flop/s * 3 s in megaflop'
5637.144576 megaFLOP

$ cpc '3 teraflops * 5 min'
900 teraFLOP

$ cpc '1.7 exaflops / 14 petaflops'
121.428571428571428571428571428571428571

FLOP⁠—Floating-point Operation⁠—(computational work) is always singular, and FLOPs⁠—Floating-point Operations per second⁠—(computational performance) is always plural. Since "FLOPs" is often used as an abbreviation for "FLOP/s", I allowed the syntax for convenience (similarly to how we can write "bps" for data rates).

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I found myself often wanting to compute stuff with FLOP/s to calculate scientific kernel performance or speedups between benchmark versions, so I figured I would contribute my changes. 🙂

[probablykasper]

Awesome!

I think the UnitType should just be Flops. Otherwise we would have trouble adding something like integer OPS, since that's also a unit of computational work, but not compatible with Flops

[dssgabriel]

I think the UnitType should just be Flops.

Do you mean simply renaming the FLOP computational work unit to Flops (and maybe describing it as floating-point computational work)?

[probablykasper]

Yeah, unless you have a better term