fix types resolution when moduleResolution is NodeNext

Two issues:

1. The `exports` map in `package.json` needs to include the `types`
key. See: microsoft/TypeScript#51996

2. Explicit `.js` extension is needed for the `export ... from`
statements in `src/index.ts` to satisfy ESM.

Point 2 in turn required a minor tweak to the import statement in
two of the tests (must import `createContainer from `./src/iti`,
not merely `./src`).

iti/package.json

@@ -7,7 +7,8 @@
   "source": "src/index.ts",
   "exports": {
     "require": "./dist/iti.cjs",
-    "default": "./dist/iti.modern.js"
+    "default": "./dist/iti.modern.js",
+    "types": "./dist/src/index.d.ts"
   },
   "main": "./dist/iti.cjs",
   "module": "./dist/iti.module.js",

iti/src/index.ts

@@ -1,11 +1,11 @@
 // Main lib
-export { createContainer, createContainer as makeRoot, Container } from "./iti"
+export { createContainer, createContainer as makeRoot, Container } from "./iti.js"
 
 // Helper types
 export type {
   GetContainerFormat,
   UnPromisify,
   UnpackFunction,
   Prettify,
-} from "./_utils"
-export type { Emitter } from "./nanoevents"
+} from "./_utils.js"
+export type { Emitter } from "./nanoevents.js"

iti/tests/dispose-graph.ts.api.spec.ts

@@ -1,5 +1,5 @@
 import { expect, jest, describe, beforeEach, it } from "@jest/globals"
-import { createContainer } from "../src"
+import { createContainer } from "../src/iti"
 import { wait } from "./_utils"
 import { A, X, B, C, D, L, K, E, M, F } from "./mock-graph"
 

iti/tests/dispose.ts.api.spec.ts

@@ -1,5 +1,5 @@
 import { expect, jest, describe, beforeEach, it } from "@jest/globals"
-import { createContainer } from "../src"
+import { createContainer } from "../src/iti"
 import { wait } from "./_utils"
 
 describe("Disposing: ", () => {