Remove trailing / from server URIs

[bfops]

If a user adds a server with trailing slash, they can get errors e.g.

Error: Unable to retrieve fingerprint for server: https://bitcraft.spacetimedb.org/
Is the server running?
Add a server without retrieving its fingerprint with:
        spacetime server add https://bitcraft.spacetimedb.org/ --no-fingerprint

Caused by:
    HTTP status client error (404 Not Found) for url (https://bitcraft.spacetimedb.org//identity/public-key)

(It ends up putting // in its URLs)

Definition of Done

The following places strip /s from server URIs before adding them and/or trying to use them:

• CLI
• Rust SDK
• C# SDK (and Unity SDK)
• TypeScript SDK

[bfops]

The Rust SDK kind of does this properly. If I pass http://localhost:3000 or http://localhost:3000/, the SDK works fine; if I pass http://localhost:3000// then it breaks, and I think that that's reasonable behavior.

[bfops]

The TypeScript SDK has similar behavior to the Rust SDK - if I pass http://localhost:3000 or http://localhost:3000/ it works, but http://localhost:3000// does not. Again I think that's reasonable behavior.