Fix encodeBase64 not handling uint8 arrays beyond ~100kB

[refi93]

Motivation: When I was trying to upload bigger data to polybase it was failing with a RangeError: Maximum call stack size exceeded which turned out to be caused by the encodeBase64() function which apparently wasn't able to handle data bigger than ~100kB.

This PR reimplements the encodeBase64() in a safer way which works with bigger arrays without issues, even beyond 1MB - not sure if there's an upper bound (in practice I expect that code to be too slow/blocking for files larger than several MB), I guess a proper solution for bigger data would be to stream/chunk it somehow which would require designing a whole new API call, nevertheless, this solution is an improvement respective to the current implementation and it was already enough for my usecase

more info on the issue e.g. here: mathiasbynens/base64#13

How to test: Try creating a colletion with a buffer field containing a data item of more than 100kB:

const pb = new Polybase({
  defaultNamespace: 'mynamespace',
})
await pb
  .collection('MyCollection')
  .create([Array(1_000_000).fill(0)]) // on main this would fail with "RangeError: Maximum call stack size exceeded"