* Move qpy to own module.

qpy_serialization.py is splint into several files for maintenability. This commit also adds several bytes Enum classes for type keys in the header, and provides several helper functions. Some namedtuple class names are updated because, for example, INSTRUCTION will be vague when we add schedule, i.e. it's basically different program and has own instruction that has different data format. Basically CIRCUIT_ prefix is added to them.

* manually cherry-pick #7584 with some cleanup

- change qiskit.qpy.objects -> qiskit.qpy.binary_io
- TUPLE -> SEQUENCE (we may use this for list in future)
- add QpyError
- add _write_register in circuit io to remove boilerplate code

* respond to review comments
- expose several private methods for backward compatibility
- use options for symengine
- rename alphanumeric -> value
- rename write, read methods and remove alias
- improve container read

* remove import warning

* replace alphanumeric with value in comments and messages.

* private functions import

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

…(#7550)

* Add support for custom metadata serializers to QPY load() and dump()

This commit adds a new argument to load(), metadata_serializer, and
dump(), metadata_deserializer, which is used to specify custom
serialization functions to use for serializing the python dictionary for
each circuit's metadata attribute. By default QPY expects the serialized
metadata payload to be encoded as a utf8 json string. But since there
are no user constraints on the metadata dictionary's contents a simple
json.dump() of the circuit's metadata attribute may not be feasible. To
address this issue these new arguments are added to enable users to
specify a custom function to encode the dictionary as binary data
however is required for their circuit's metadata and then read that
custom format as required when deserializing.

The QPY format specification does not change here and still explicitly
lists a UTF8 encoded JSON string as the contents. A fixed format is
needed in the format specification for potential interoperability for
other tools generating QPY data (none exist currently to my knowledge
but nothing precludes it which is why the format is publicly
documented). These new arguments are specific to only the qiskit
implementation and should only be used when generating qpy files and
loading them via qiskit.

* Pivot to use JSONEncoder and JSONDecoder classes for new argument

This commit pivots to leveraging custom JSONEncoder and JSONDecoder
classes for the optional serializer and deserializer arguments instead
of custom callables that return bytes. In the previous commit we used
callables that would be passed the dictionary and returned bytes.
However, while this was flexible it was pretty easy for a user to create
QPY out of spec. While this was documented it is probably easier to just
constrain the argument to always producing valid json. Using custom
encoder and decoder classes let users still handle custom types but also
restrict things to always be JSON. This should fix the potential risk in
the previous iteration but still fix the underlying issue.

* Update release note

* Remove pylint ignores from release note example

Co-authored-by: Jake Lishman <[email protected]>

Co-authored-by: Jake Lishman <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>