Chore: switch to node 18

[dario-piotrowicz]

We are currently using node 16 for developing the package, 16 has been deprecated in September, so we should switch to just using 18 moving forward.

This involves:

• developing the package using 18 and making sure that everything still works
• updating our dependencies and everything that might be related to 16
  (in particular, the node-fetch dependencies we have should be removed since in 18 fetch is built in into node)
• updating our readmes and the cloudflare docs asking users to use 18+

Note

Since this might effect existing users/applications it needs to be done in the next major release

[dario-piotrowicz]

This is blocked by: #623 (and #648) since node-fetch is being used in the setupDevBindings utility, so we first need to update such utility (which can also remove the node-fetch dependency)