add named export for main Turnstile component

[EmilePerron]

This adds a named export Turnstile for the main component, which is the same as the default export, and bumps the version to 1.1.5.

The reason for this is that modern tools like Rolldown wrecks / reformats exports of libraries that have both a default export and named exports, leading to the following error:

Uncaught Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.

This behaviour is likely the root cause behind issue #24.

Providing a named export and making this the suggested way to consume the exports gives users a way out of this behaviour. The existing default export is still kept as is to maintain backwards compatibility.