[Core] Other Pylint Fixes

[Kashif Khan (kashifkhan)]

Part 2 of next-pylint fixes - these focus on adding some more disables, simplifying if/elif statements, asserts on empty objects

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[azure-pipelines]

Azure Pipelines:
Successfully started running 3 pipeline(s).
8 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[Copilot]

Pull request overview

Addresses Pylint findings across Azure Core tests, test infrastructure, and samples.

Changes:

• Simplifies assertions, branches, comprehensions, and resource handling.
• Adds targeted Pylint suppressions and missing imports.
• Removes unreachable code and adds licensing metadata.

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/utils.py	Uses idiomatic method type checking.
tests/testserver_tests/coretestserver/coretestserver/test_routes/xml_route.py	Simplifies route branching.
tests/testserver_tests/coretestserver/coretestserver/test_routes/helpers.py	Adds Base64 import and simplifies helpers.
tests/test_universal_pipeline.py	Suppresses statement-count warning.
tests/test_tracing_policy.py	Suppresses transport import warning.
tests/test_testserver.py	Suppresses transport import warning.
tests/test_streaming.py	Suppresses transport import warning.
tests/test_stream_generator.py	Handles exhausted reads explicitly.
tests/test_serialization.py	Simplifies branches and assertions.
tests/test_retry_policy.py	Improves temporary-file handling and assertions.
tests/test_rest_stream_responses.py	Simplifies stream collection and property access.
tests/test_rest_response_backcompat.py	Suppresses transport import warning.
tests/test_rest_http_response.py	Suppresses response import warning.
tests/test_rest_http_request.py	Simplifies iterator and header assertions.
tests/test_rest_headers.py	Simplifies empty-header assertion.
tests/test_requests_universal.py	Suppresses transport import warning.
tests/test_pipeline.py	Suppresses transport import warning.
tests/test_paging.py	Removes unnecessary else branches.
tests/test_exceptions.py	Simplifies empty-value assertions.
tests/test_basic_transport.py	Suppresses transport import warning.
tests/test_base_polling.py	Simplifies mock dispatch branches.
tests/specs_sdk/modeltypes/modeltypes/_utils/model_base.py	Revises optional-type detection.
tests/perf_tests/_test_base.py	Suppresses transport import warning.
tests/async_tests/test_universal_http_async.py	Removes unreachable assertion.
tests/async_tests/test_testserver_async.py	Suppresses transport import warning.
tests/async_tests/test_stream_generator_async.py	Suppresses transport import warning.
tests/async_tests/test_retry_policy_async.py	Improves file handling and assertions.
tests/async_tests/test_rest_trio_transport.py	Suppresses transport import warning.
tests/async_tests/test_rest_stream_responses_async.py	Simplifies asynchronous stream collection.
tests/async_tests/test_rest_response_backcompat_async.py	Suppresses transport import warning.
tests/async_tests/test_rest_http_response_async.py	Suppresses module import warning.
tests/async_tests/test_rest_http_request_async.py	Simplifies header assertions.
tests/async_tests/test_rest_headers_async.py	Simplifies empty-header assertion.
tests/async_tests/test_rest_asyncio_transport.py	Suppresses transport import warning.
tests/async_tests/test_request_trio.py	Preserves exception chaining.
tests/async_tests/test_request_asyncio.py	Suppresses transport import warning.
tests/async_tests/test_pipeline_async.py	Suppresses transport import warning.
tests/async_tests/test_paging_async.py	Removes unnecessary else branches.
tests/async_tests/test_http_logging_policy_async.py	Suppresses statement-count warnings.
tests/async_tests/test_basic_transport_async.py	Removes unnecessary f-strings.
tests/async_tests/test_base_polling_async.py	Simplifies mock dispatch branches.
samples/test_example_sync.py	Suppresses protected-access warning.
samples/test_example_sansio.py	Suppresses protected-access warning.
samples/test_example_async.py	Suppresses protected-access warning.
samples/example_tracing_async.py	Adds the standard license header.