Generalize core primitives to abstract number type

We can turn `circle :: ℝ -> SymbolicObj2` into e.g. `circle :: Num a => a -> SymbolicObj2 a`.

That would allow us to use different numerical types instead of being fixed on `Doubles`. Some fun examples include
- discrete type like `Integer`
- arbitrarily precise `CReal` from https://hackage.haskell.org/package/exact-real
- symbolic `Sym` from https://hackage.haskell.org/package/numbers-3000.2.0.2/docs/Data-Number-Symbolic.html
- `ℝ` from https://github.com/Haskell-Things/ImplicitCAD/pull/225
- types with dimensions (`units` or `dimensional`)

It would also open a lot of doors to other backends like `accelerate` or `GLSL`, where symbolic objects could be represented as, well.. symbolic functions.

Also an analytical simplification step could be implemented before actual discretization and evaluation which could drastically improve performance for some cases.