Cardano Updates

Signed-off-by: Sasha Bogicevic <[email protected]>

Signed-off-by: Ales Verbic <[email protected]>

Signed-off-by: etorreborre <[email protected]>

Signed-off-by: etorreborre <[email protected]>

instead of being a child of the `middleware` file and module

- fix/enhance some doc comments and logs
- use u64 everywhere for offset configuration and parsing
- `expand_epoch`:
  - use const value from `"latest".len()` instead of `7`
  - tests: add decimal cases

Cardano Stake Distribution signed entities are created with an offset of
`-1` to the epoch, this must be reflected to the epoch expansion when
using `latest` (with or without additional offset).
Else querying with `latest` will always returns a `404`.

... when the epoch service is unavailable

Where epoch can be either a integer, `latest`, or `latest-{offset}`

Actual epoch retrieval is done with a async lambda to give flexibility
to the caller so they may do it beforehand or make the expander perform
the operation.

- Add a indexed `epoch` virtual column to `signe_entity` table, computed
  from the discriminant beacon
- Supersed `GetSignedEntityRecordQuery::cardano_stake_distribution_by_epoch`
  with a `by_signed_entity_type_and_epoch` method that works on any
  discriminant
- strengthen `GetSignedEntityRecordQuery` tests & tooling

To avoid collision when stored in a database

Instead of lists, since most of the time we only need one value and it's
cubersome to extract it from the generated Vec.

Signed-off-by: Chris Gianelloni <[email protected]>