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

etc/eslint.config.mjs

@@ -0,0 +1,14 @@
+import {defineConfig} from 'eslint/config'
+import js from '@eslint/js'
+import globals from 'globals'
+
+export default defineConfig([{
+   files: ['**/*.js'],
+   plugins: {js},
+   languageOptions: {globals: {...globals.mocha, ...globals.node}},
+   extends: ['js/recommended'],
+   rules: {
+      'no-unused-vars': ['error', {argsIgnorePattern: '^_'}],
+      'no-empty': ['error', {allowEmptyCatch: true}],
+   }
+}])