Remove obsolete Python 3.10 compatibility code #3374

Python 3.10 support has been dropped, but the repository has not yet had a sweep to remove code retained solely for Python 3.10 compatibility.

Audit the repository and remove obsolete compatibility branches, fallbacks, helpers, and comments where the supported Python versions provide the required functionality directly. Preserve compatibility with all currently supported Python versions.

Known examples surfaced in #3230:

• The exception-note helper in cuda_core/tests/memory_ipc/test_vmm_fabric.py combines the exception message with __notes__ to accommodate Python 3.10.
• The fabric allocation probe in cuda_core/tests/conftest.py also handles exception notes appended to the message on Python 3.10.

The two examples may be cleaned up in #3230; this issue tracks the broader sweep.

Acceptance criteria:

• Audit Python-version guards and compatibility comments across the repository.
• Remove code needed only for Python 3.10 and simplify affected callers and tests.
• Run the relevant checks for affected packages on supported Python versions.

Related: #2163 (Python 3.15 support and dropping Python 3.10), #2198 (Python 3.10 support announcement), and the review comments on #3230.