Implement compression of objects before they are saved into the storage
provider. Each container type can specify which algorithm to use
(currently `none` or `zstd`) and the compression level.
Consolidate the saving of object dependencies and saving the actual
objects' data into a single function called `add_objects`. The previous
methods `add_dependencies`, `add_custom_invalidation_data` and `put`
have been removed.
Optimize the `run` function to skip objects that have just been
serialized when deserializing objects for outgoing requests. For
example, previously if a schedule had for a savepoint:
```yaml
incoming: ["/binary"]
outgoing: ["/binary"]
```
then the `Savepoint.run` function would have first serialized the object
into storage and then deserialized it right after, instead with the new
function the object is only serialized.
Giacomo Vercesi