ReadableSpan events and links now return a tuple

[Arnatious]

Description

ReadableSpan events and links attributes now return a sequence, as described, removing a TypeError.

No longer attempt to wrap Links and Events in MappingProxy's since they are not descendants of Mapping like Attributes.

Fixes #2214

Type of change

Please delete options that are not relevant.

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

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Ran tox -e py38-opentelemetry-sdk -- trace/test_trace.py::TestReadableSpan (tested on Python 3.8.10 on Ubuntu on WSL2)

Does This PR Require a Contrib Repo Change?

Answer the following question based on these examples of changes that would require a Contrib Repo Change:

• The OTel specification has changed which prompted this PR to update the method interfaces of opentelemetry-api/ or opentelemetry-sdk/

• The method interfaces of test/util have changed

• Scripts in scripts/ that were copied over to the Contrib repo have changed

• Configuration files that were copied over to the Contrib repo have changed (when consistency between repositories is applicable) such as in

  • pyproject.toml
  • isort.cfg
  • .flake8

• When a new .github/CODEOWNER is added

• Major changes to project information, such as in:

  • README.md
  • CONTRIBUTING.md

• 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 are authorized under a signed CLA.

• ✅ Ted Kern (dd49d29)

[ocelotl]

I think this PR needs a changelog entry ✌️

[Arnatious]

Added changelog entry!

[ocelotl]

Please fix lint and we can get this merged in, @Arnatious ✌️

[Arnatious]

Re:fixed lint, looks like I missed whitespace first time.

Separate issue I'll raise: tox -e lint fails because of

ERROR: Cannot install httpretty because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested httpretty
    The user requested (constraint) httpretty~=1.0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies

[ocelotl]

Here is how to fix black and isort lint problems:

0. cd to the root of the opentelemetry-python repo
1. tox -e lint
2. source .tox/lint/bin/activate
3. black .
4. isort .
5. deactivate

Commit the generated changes.