Refactor serialization

[bolkedebruin]

This refactors serialization so it is now modular and allows for extending. It implements versioning and allows namespace packages to be added to allow custom serializers for third-party objects.

This should replace all other serializers (eventually, only DAG remains).

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in newsfragments.

[kaxil]

yeah this is needed for things like below:

In [1]: import numpy

In [2]: numpy.int64(2)
Out[2]: 2

In [3]: type(_2)
Out[3]: numpy.int64

In [4]: type(_2).__qualname__
Out[4]: 'int64'

In [5]: type(_2).__module__
Out[5]: 'numpy'

In [6]: _2.__qualname__
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Input In [6], in <cell line: 1>()
----> 1 _2.__qualname__

AttributeError: 'numpy.int64' object has no attribute '__qualname__'

In [7]: _2.__module__
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Input In [7], in <cell line: 1>()
----> 1 _2.__module__

AttributeError: 'numpy.int64' object has no attribute '__module__'

[kaxil]

Should we try to get it from version too as a fallback? as that was shipped with 2.5?

[kaxil]

Suggested change

	VERSION: getattr(cls, "__version__", DEFAULT_VERSION),
	VERSION: getattr(cls, "__version__", getattr(cls, "version", DEFAULT_VERSION)),

[bolkedebruin]

Yes it was shipped, but nowhere implemented, so only custom classes after that could use this. Some of the providers collide with version (e.g. ggoogle) so we are obtaining the wrong version then. So I'd prefer to take the small hit and this is PEP 8/480 compatible.

[uranusjr]

Since this is only really used by SerializedDAG, I think it’s more productive to simply have deserialize(...) -> Any and add a separate deserialize_dag(...) -> SerializedDAG that simply calls deserialize internally and provide a better return type hint.

[bolkedebruin]

It is not only used by SerializedDAG (why do you think so?) it will be used by XCom too (which is even the first implementation). deserialize_dag will be removed as it is non-standard.