[Aurora-L6]

An application-installed, unnamed logging.StreamHandler or logging.NullHandler makes MetaSchedule task logger initialization fail with AttributeError: 'NoneType' object has no attribute 'format'. create_loggers includes the handler's default None name in references that are later formatted as strings.

Skip unnamed existing handlers when constructing those named references. Add a subprocess-isolated regression covering both handler types and a no-handler control; each case initializes twice and verifies messages in both task log files.

Fixes #20828.

Validation on macOS arm64, Python 3.12.11, with a clean CPU-only build of TVM main (e345029c):

• Before the fix: the two unnamed-handler cases fail with the reported AttributeError; the no-handler control passes.
• After the fix: the three regression cases and two adjacent MetaSchedule profiler tests pass (5 passed).
• pre-commit run --files python/tvm/s_tir/meta_schedule/logging.py tests/python/s_tir/meta_schedule/test_meta_schedule_logging.py: all applicable hooks pass.