Add ItemType validation to the various keystores

We have this potentially doable TOOD in the ephemeral keystore:

// TODO: add item_type validation to Keystore::get and Keystore::remove.
// The presence of a key with a mismatched item_type can be either due to keystore
// corruption, or API misuse. We will need a new error type and corresponding ErrorKind for
// that).
//
// TODO: add item_type validation to ArtiNativeKeystore

The TODO asks is about adding extra validation to each operation of each Keystore impl.

added Doing label

Assigned to @hashcatHitman as we chatted about this over email.

Hi. There's already !2897 (closed) open that tries to resolves the second TODO.

Hi playbahn,

I don't think that's an issue at the moment. I saw your MR and decided to focus on the first TODO, since that is the one gabi and I have spoken about mostly (as I understand it, anyway). Thanks for the heads up, though.

In that case, go ahead!

mentioned in merge request !2917 (merged)

mentioned in commit 5a95fcb4

closed with merge request !2917 (merged)