It seems you can do that even without any third party library like 7zip:
WebClient OpenRead will get you a stream from your URI and ZipArchive constructor from stream will get you a ZipArchive from it:
var uri = @"https://myaccount.file.core.windows.net/shared1/folder1/data00054.zip";
var wc = new WebClient();
var stream = wc.OpenRead(uri);
var zip = new ZipArchive(stream);
Apply using-blocks as appropriate.
If you really really want to use the third party library, you can find the documentation (in this case, the source) here. As you can see, it can work with arbitrary streams as well:
var uri = @"https://myaccount.file.core.windows.net/shared1/folder1/data00054.zip";
var wc = new WebClient();
var stream = wc.OpenRead(uri);
var extractor = new SevenZipExtractor(stream);