feat: Only export as ESM.

[ShogunPanda]

This PR changes Lyra to be a ESM only package, since most of our target runtime support ESM by default.
For CJS compatibility, a separate export point is exported which can be used to require Lyra in both the following ways:

const { create, insert } = require('@lyrasearch/lyra/cjs')

create()
  .then(db => insert(db, {/* ... */})
  .catch(console.error)

OR

const { requireLyra } = require('@lyrasearch/lyra/cjs')

requireLyra((err, lyra) => {
  if(err) {
    throw err
  }

  const { create, insert } = lyra
  create()
    .then(db => insert(db, {/* ... */})
    .catch(console.error)
})

Note that tokenize and formatNanoseconds are not export anymore in index.ts nor cjs since they are not async methods.

[micheleriva]

LGTM