Improve some miscellaneous type annotations

[mfisher87]

Description

I just had these changes sitting around in my working copy for some reason. Figured I should just commit them!

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📚 Documentation preview 📚: https://earthaccess--1440.org.readthedocs.build/en/1440/

[github-actions]

👈 Launch a binder notebook on this branch for commit fb3dd10

I will automatically update this comment whenever this PR is modified

👈 Launch a binder notebook on this branch for commit 588db95

👈 Launch a binder notebook on this branch for commit 004a8d6

👈 Launch a binder notebook on this branch for commit f7eef07

[mfisher87]

I don't like all these type guards, but if we want to type check this code we need them because of this line -- self.auth can be None. I'd rather not do this, but the purpose of this PR is to add type information, not change behavior.