d0b9405f96 Refactors `keystore.h` type aliases. (251)
Pull request description:
This pull request frees `keystore.h` from type alias declarations that have been declared at file scope level.
`keystore.h` has various type aliases that have been declared ~3 - 6 years ago at file scope level, which can either be encapsulated or removed.
Where type alias declarations are encapsulated at the appropriate scope and access level, C++11's `using` notation is used in favor of the `typedef` notation.
Tree-SHA512: 1395cdc63e0c7ff5a1b1721675ad4416f71f507e999bd4ba019f03457cbfc08877848f10a8db7f5ccd2cd5ca3f5a291c986616f7703172fb6d79fba7447ffba8
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