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.
Change byte containers from being just a `using` of the relative class
(e.g. `BytesContainer`) to a full fledged subclass. This has the
following benefits:
* The template arguments are now laid out in the container class body,
making it more readable.
* The creation of a new class creates a new symbol, improving
debuggability as now the container classes have their own name rather
than the expanded base class template.
Generalize `FunctionStringMap` into `detail::GenericStringMap`, which
supports any `Depth=1` rank. `FunctionStringMap` remains as an `using`
with `Rank = ranks::Function`.
Replace the stub implementation of invalidation with the proper
implementation. A ReadPathCache is added to each global so that it can
keep tracks of what target are associated to which read paths.
Change the serialization and deserialzation functions of
`FunctionStringMap` to use the GzipTarFile. Also change che filename
of the underlying containers accordingly.
A logic issue existed in the Pipe, as it was mistakenly relying on
`IsolatedRoot` instead of the isolated function. That was breaking
things if those functions were to be removed. This issue has been
addressed by correcting the behaviour of the Pipe.
Giacomo Vercesi