* Refactor obtaining of activation heights
* Impl the `RegisterKeys` service request
* Mock viewing keys for tests
* Refactor tests
* Apply suggestions from code review
Co-authored-by: Arya <aryasolhi@gmail.com>
* Remove a redundant comment
I don't think we need to assume the genesis block doesn't contain
shielded data as the comment says.
* Avoid using a single-letter variable
* Refactor mocking Sapling scanning keys
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Co-authored-by: Arya <aryasolhi@gmail.com>