Improve usability by adding two convenience libraries

Currently, if I want to create say one meter, I always need to write: `Length.Of(1, Si())`.

This is semantically clean but a tad verbose. Hence create two convenience libraries
- Atmoos.Quantities.Convenience
- Atmoos.Quantities.Units.Convenience

that would expose types that'd enable the following syntax:

```csharp
Length oneMetre = 1 * m;

Velocity oneKpH = 1 * km/h;

// similary,
var oneSecond = 1 * s;
var threeOhm = 3 * Ω;
```