Extract temporary and permanent storage changes

[thpani]

Preparatory change towards #54.
Closes #121
Closes #126

In the fetcher, extract all ledger entry changes from a transaction, i.e, including

• changes to temporary and persistent storage, and
• changes to other contracts than the (root-)invoked contract.

The result is two (pre- & post-state) nested maps keyed by

1. contract address
2. 'instance' | 'persistent' | 'temporary'
3. the ScVal key, SDK-transformed to a native JS val and .toString()ed

The resulting maps are only propagated to Solarkraft on-disk storage, and not yet used for instrumentation. In particular, we still populate fields and oldFields by projecting the above maps to the instance storage of the root-invocation contract ID.

Tests:
Update the setter contract to store all fields in instance, persistent and temporary storage.

Note that the presence of fields is different between instance and persistent/temporary:
instance is a single LedgerEntry, thus all instance fields are present if a single instance field changes.
persistent/temporary have one LedgerEntry per field, thus they are only present in the transaction if that field is changed.

We should follow up with case studies to determine user needs:

• Evaluate user needs for presence of storage fields #128

[konnov]

Looks good. Absence of tests worries me a bit though :)

[thpani]

Looks good. Absence of tests worries me a bit though :)

Oh, I didn't notice I requested a review already 😅
I'll still add tests, just wanted to save the progress before my vacation.

[thpani]

@konnov I've added persistent/temporary fields in the setter contract and to the tests.
More details on persistent/temporary behavior in the PR desc.

PTAL