Fix importing in CJS nodejs by adding conditional export

[davidyuk]

This PR is supported by the Æternity Foundation

I discovered that the recent calldata package can't be imported into a CJS file in nodejs.

// test.cjs
const { Encoder } = require('@aeternity/aepp-calldata');

console.log('Encoder', Encoder);

fails with

Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in /.../test-aeproject-2/node_modules/@aeternity/aepp-calldata/package.json

using nodejs@20.18 and @aeternity/aepp-calldata@1.9.0. Looks like "type": "module", in package.json we added recently enabled the usage of exports instead main in this case 👉 👈