Make mandatory session properties immutable

[interpretor]

Closes #2.

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• issue number linked above after pound (#)
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Attach a session object to the event context with mandatory immutable properties id, createdAt and ip.
When the user wants to reassign those properties, an error is thrown. This is better than just doing nothing, because the user knows that he did something wrong in saving properties to the session in the event context.

[BracketJohn]

and, sorry to kind of push this in here, but as we're already working on the Session interface: Would you consider adapting the h3 event context as done here:
https://github.com/sidebase/nuxt-prisma/blob/b1ffd717cf1061215498fa8e9b90ce62cac8b494/src/runtime/server/middleware/prisma.ts#L7-L11

whuile you're add it? This way, typing for the end-user should improve when they access event.context.session

[interpretor]

Added it, but somehow the types aren't available when packed and imported as module in a project. Any suggestions?