feat: factories can depend on the presence of types

Refactors each TypeDispatcher to have its own separate collection
  of types. Add isnan function which returns a boolean if that type
  is present, otherwise returns the number 1 for true, and 0 for fase.

src/number/type.js

@@ -1,4 +1,4 @@
-import {plain} from './helpers.js'
+import {plain, boolnum} from './helpers.js'
 import {BooleanT} from '#boolean/BooleanT.js'
 import {Returns} from '#core/Type.js'
 import {NumberT} from '#number/NumberT.js'
@@ -7,6 +7,6 @@ const num = f => Returns(NumberT, f)
 
 export const number = plain(a => a)
 number.also(
-   BooleanT, num(a => a ? 1 : 0),
+   BooleanT, boolnum,
    [], num(() => 0)
 )