feat: Index behaviors by return typing strategy

* Adds the concept of, and options for, the return typing strategy
  * adds the strategy at the beginning of every behavior index
  * adds the strategy as an additional argument to resolve
  * No actual use of return type strategy so far
  * Sets up eslint
  * Fixes eslint errors

src/number/utils.js

@@ -1,7 +1,6 @@
 import {plain, boolnum} from './helpers.js'
 import {NumberT} from './NumberT.js'
 
-import {Returns} from '#core/Type.js'
 import {match} from '#core/TypePatterns.js'
 
 export const clone = plain(a => a)