Add comments about assertions that use JS BitInts

[bushidocodes]

A student might not be familiar with the JavaScript type system, which bleeds through via the n suffix in the test that get logged to console. Investigate ways to document or clarify that this is a wasm i64.

CODE RUN

let resultSigned = currentInstance.exports.square(1n);
let resultUnsigned = BigInt.asUintN(64, resultSigned);
expect(resultUnsigned).toEqual(1n);

TEST FAILURE

Error: expect(received).toEqual(expected) // deep equality

Expected: 1n
Received: 42n