Fix memory leak in exporter and reader

[msoltysik]

Description

This PR addresses memory leak issue in the exporter and reader by using the weakref library.

The solution, proposed by @aabmass, utilizes weakref.WeakMethod and weakref.WeakSet to ensure proper garbage collection and prevent unintended object retention.

Discussion can be found in the following issue - Fixes #4220

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

It has been covered by a test case.

============================= test session starts ==============================
collecting ... collected 1 item

test_provider_shutdown.py::TestMeterProviderShutdown::test_meter_provider_shutdown_cleans_up_successfully PASSED [100%]

============================== 1 passed in 0.08s ===============================

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: msoltysik / name: Mateusz Soltysik (c51244f, 83d06b0, 5ed8da9, 328085e, 4b68c87, 0f940f7, 89a11c0, 7b20bf8, d84bf56, 5bde8d7)
• ✅ login: emdneto / name: Emídio Neto (84c6b0a)

[xrmx]

@msoltysik please fix ruff failure

[msoltysik]

Hey @xrmx , I've just applied tox -e ruff

[emdneto]

Thanks. The test fails against main. LGTM