* `ValueAggregate` refactoring
0. Service results, canon results and literals are constructed as
separate types that are further wrapped with `ValueAggregate`.
1. `ValueAggregate` is enum that contains all the provenance info.
2. Construction methods get provenance information as well.
* Rename CID state field
Prepare to adding a canon CID field: rename `canon_tracker`/`canon_store`
to `canon_element_tracker`/`canon_element_store`.
* Add canon result store/tracker
* Rename some structs that have CIDs inside
Reflect explicitly that they contain CIDs inside:
`CanonResultAggregate` -> `CanonResultCidAggregate`
`ServiceResultAggregate` -> `ServiceResultCidAggregate`
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Co-authored-by: Mike Voronov <michail.vms@gmail.com>
Many internal structures refer to trace positions; this is an important type of values. In the code, it is sometimes `u32`, sometimes `usize`. While such variables usually have "_pos" suffix, having a dedicated type does improve code with type guarantees.
Intially, a fold instruction was designed based on idea that its iterable can't expand,
so AIR was considered as a subtree. But after introducing recursive streams in #225, it's
no more a subtree, but a subgraph.
