ref(o11y): Add scope.set_attribute in authentication

[sentrivana]

• Supplements existing scope.set_tag() calls with equivalent scope.set_attribute() calls in src/sentry/api/authentication.py
• This enables attributes-based telemetry (logs, metrics, spans v2) to inherit these values
• Handles type mismatches: guards None entity_id and decodes bytes token_name

Once we switch to span streaming, the new attributes will get applied to spans automatically.

Related to getsentry/sentry-python#6537

[cursor]

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[github-actions]

Backend Test Failures

Failures on 82e41ab in this run:

tests/sentry/api/helpers/test_deprecation.py::TestDeprecationDecorator::test_with_url_names — log

[gw0] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/api/helpers/test_deprecation.py:243: in test_with_url_names
    assert resp.status_code == HTTP_200_OK
E   assert 410 == 200
E    +  where 410 = <Response status_code=410, "text/html; charset=utf-8">.status_code