fix(storage): honor timeout in upload_chunks_concurrently - #18765

Fixes #18764

upload_chunks_concurrently takes a timeout argument and documents it as the time to wait for the server response, but it never passed it on. The XML multipart requests it makes (initiate, each part upload, finalize, and cancel when something fails) all ran with the (61, 60) default of the media layer, so a caller could not make a stuck upload fail sooner or give a slow connection more time.

This passes timeout to XMLMPUContainer.initiate, finalize and cancel, and adds it to the _upload_part worker so every XMLMPUPart.upload gets it as well. Thread and process workers behave the same, since the timeout is a plain number or tuple.

One small change for callers who don't pass a timeout: these requests now use the documented default of 60 seconds (_DEFAULT_TIMEOUT, the value every Blob upload and download already sends) instead of (61, 60). Only the connect timeout moves, by one second.

The cleanup cancel gets the same timeout as the other requests. If the cancel itself fails, for example with a very short timeout, the failure is logged as a warning with the upload id and the original upload error is still the one raised. test_upload_chunks_concurrently_keeps_original_error_when_cancel_fails covers that path.

With the script from the issue, which records the timeout each request gets:

main                            this branch
initiate     timeout=(61, 60)   initiate     timeout=5
upload part  timeout=(61, 60)   upload part  timeout=5
upload part  timeout=(61, 60)   upload part  timeout=5
finalize     timeout=(61, 60)   finalize     timeout=5

Added test_upload_chunks_concurrently_passes_timeout and test_upload_chunks_concurrently_passes_timeout_to_cancel, which fail on main and pass with this change. The existing tests that checked these calls now also check that the default timeout is sent, and test__upload_part checks that the worker hands its timeout to the part upload. The full tests/unit suite passes locally (2068 passed), and the noxfile's ruff==0.14.14 import and format checks and flake8 report nothing.

• Issue opened before writing the code (storage: upload_chunks_concurrently ignores its timeout argument #18764)
• Tests and linter pass
• Code coverage does not decrease
• No docs changes needed