Result<Option<>> rather than Option<Option<>>

[gilescope]

Meme driven development: You are using a three state enum rather than Option<Option<>> right? right???

Edit: No, we're going to use Result<Option<>>

[coriolinus]

Seems like a good idea, but needs a bit more work before it's ready.

[gilescope]

(I came across an ICE when coding this - but rust-lang/rust#86368 fixes it and should be in nightly soon)

[shawntabrizi]

@gilescope what public runtime APIs does this break?

[gilescope]

@shawntabrizi in primitives/runtime/src/offchain/storage.rs these are the breaking changes:

StorageValueRef::get returns Result<Option<T>> rather than Option<Option<T>>.
StorageValueRef::mutate returns Result<T, MutateStorageError> rathern than a Result<Result<T>> (and also the closure it accepts now takes a Result<Option<T>> rather than an Option<Option<T>>.

They make the api easier to understand.

[gilescope]

Hmm, think I need to rebase.

[gilescope]

@bkchr can I get an approve from you and can I get an A6-mustntgrumble from you @coriolinus ?
(Had to bump the lock file to make the build happy, but that should be fine as it won't compile with any earlier version - trie-db really should have bumped the middle digit if it was following semver as they added a function).