fix: support exactOptionalPropertyTypes on client SDKs

[mnahkies]

previously we were always treating it as false, rather than using the value we read from the tsconfig.json file. this was intentional at the time in #131

• For typescript-koa include | undefined on optional properties when exactOptionalPropertyTypes is configured
  • This shouldn't be required for the clients, as in this case the consumer can choose to omit keys
    • Though maybe it's more ergonomic to follow this behavior anyway?

However it turns out this can cause issues with the zod schemas when runtime validation is enabled, and so it's better to follow this | undefined pattern on the clients as well. It's probably more ergonomic as well tbh.