Better handling for described encoding

[fafhrd91]

Description

1. Current implementation drops "descriptor" for described types.
   This pr keeps descriptor as "descriptor" attribute.
2. Fix decoding for array of described types

All SDK Contribution checklist:

• [*] The pull request does not introduce [breaking changes]
• [ *] CHANGELOG is updated for new features, bug fixes or other significant changes.
• [ *] I have read the contribution guidelines.

[Copilot]

Pull request overview

Improves AMQP described-type decoding in the Event Hubs pyamqp stack by preserving the descriptor on decoded values and fixing decoding for arrays whose element type is described.

Changes:

• Adds described-value wrapper types (e.g., DescribedList) to retain a .descriptor attribute on decoded values.
• Updates array decoding to correctly handle arrays of described element types (small + large).
• Extends unit tests to cover described values and arrays of described values.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
sdk/eventhub/azure-eventhub/tests/pyamqp_tests/unittest/test_decode.py	Adds tests for described decoding and described arrays.
sdk/eventhub/azure-eventhub/azure/eventhub/_pyamqp/described.py	Introduces wrapper subclasses used to attach .descriptor to decoded values.
sdk/eventhub/azure-eventhub/azure/eventhub/_pyamqp/_decode.py	Updates described decoding and array decoding; introduces constructor→wrapper mapping.

Comments suppressed due to low confidence (1)

sdk/eventhub/azure-eventhub/azure/eventhub/_pyamqp/_decode.py:325

• In _decode_described_array, _COMPOSITES maps descriptor -> string (e.g., "accepted"), but the code uses cast(int, _COMPOSITES[descriptor]) and stores it in composite_type. This cast is incorrect/misleading for type checking and makes the variable name confusing. Update the cast/type annotation (likely str) and/or rename the variable to reflect it holds a composite name/key, not an int type code.

    try:
        composite_type = cast(int, _COMPOSITES[descriptor])
        return buffer, {composite_type: value}
    except KeyError:

[Copilot]

This only attaches .descriptor for constructors listed in _DESCR_BY_CONSTRUCTOR; for any other described underlying type (e.g., uuid/decimal128/bool/null), the descriptor is still dropped via the KeyError path. If the intent is to preserve the descriptor for all described values (per PR description), consider adding a generic fallback wrapper that stores (descriptor, value) when a specialized subclass wrapper is not available.

[kashifkhan]

/azp run python - eventhub - tests