fix: adjust export map to be actually importable

[pieh]

Which problem is this pull request solving?

With current export map I am unable to actually import from @netlify/blobs. Both CJS and ESM ( https://gist.github.com/pieh/273d2341d3623a55b33069260e6fdaac ) are failing with

> node test.mjs
node:internal/errors:497
    ErrorCaptureStackTrace(err);
    ^

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in /Users/misiek/test/netliblob-test/node_modules/@netlify/blobs/package.json imported from /Users/misiek/test/netliblob-test/test.mjs
    at new NodeError (node:internal/errors:406:5)
    at exportsNotFound (node:internal/modules/esm/resolve:268:10)
    at packageExportsResolve (node:internal/modules/esm/resolve:542:13)
    at packageResolve (node:internal/modules/esm/resolve:772:14)
    at moduleResolve (node:internal/modules/esm/resolve:838:20)
    at defaultResolve (node:internal/modules/esm/resolve:1043:11)
    at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:383:12)
    at ModuleLoader.resolve (node:internal/modules/esm/loader:352:25)
    at ModuleLoader.getModuleJob (node:internal/modules/esm/loader:228:38)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/module_job:85:39) {
  code: 'ERR_PACKAGE_PATH_NOT_EXPORTED'
}

Node.js v20.8.0

Describe the solution you've chosen

Following https://www.typescriptlang.org/docs/handbook/esm-node.html#packagejson-exports-imports-and-self-referencing

Describe alternatives you've considered

Using following export map

  "exports": {
    ".": {
      "require": "./dist/main.cjs",
      "import": "./dist/main.js",
      "default": "./dist/main.js",
      "types": "./dist/main.d.ts"
    }
  },

but it was sharing types, which while should be exactly the same, approach in PR seems safer

Checklist

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