opt(schema): Load schema and types using Stream framework

[mangalaman93]

For big datasets, we're seeing a big slowdown due to loading schema and types serially using a single iterator. Using the Stream framework, makes this metadata loading step much faster, resulting in a much faster Alpha initialization.

(cherry picked from commit d03d5ad)

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[coveralls]

Coverage: 66.611% (+0.2%) from 66.44% when pulling 6d9c83e on aman/schema into 2aed52e on main.

[harshil-goel]

LGTM. Left a question.
I feel like the stream framework api is a bit weird. Like we should be just passing the KeyToList function in the object creation itself? What do you think, maybe we should take a look at all the apis that badger has exposed.