Feature/public default stream methods

[Monishver11]

Description

Makes _legacy_default() and _per_thread_default() class methods public by removing the leading underscore, providing users with a clean API for accessing default streams.

Changes

• Renamed _legacy_default() → legacy_default()
• Renamed _per_thread_default() → per_thread_default()
• Added comprehensive docstrings explaining stream synchronization behavior
• Updated internal callers to use new public methods
• Updated existing tests to use public API
• Added new tests: test_stream_legacy_default_public_api() and test_stream_per_thread_default_public_api()

Motivation

Previously, users had to use the undocumented workaround Stream.from_handle(0) to access the legacy default stream. This PR provides official, documented class methods for accessing both default stream types.

Testing

• All existing tests pass with updated method names (33/33 tests passing)
• New tests verify public API functionality
• Subclassing behavior preserved and tested

(cuda-python-dev) [mc10322@cuda5 cuda_core]$ pytest tests/test_stream.py -v
============================================== test session starts ==============================================
platform linux -- Python 3.10.19, pytest-9.0.2, pluggy-1.6.0 -- /scratch/mc10322/miniconda3/envs/cuda-python-dev/bin/python3.10
cachedir: .pytest_cache
rootdir: /scratch/mc10322/cuda-python/cuda_core
configfile: pytest.ini
collected 33 items

tests/test_stream.py::test_stream_init_disabled PASSED                                                    [  3%]
tests/test_stream.py::test_stream_init_with_options PASSED                                                [  6%]
tests/test_stream.py::test_stream_handle PASSED                                                           [  9%]
tests/test_stream.py::test_stream_is_nonblocking PASSED                                                   [ 12%]
tests/test_stream.py::test_stream_priority PASSED                                                         [ 15%]
tests/test_stream.py::test_stream_sync PASSED                                                             [ 18%]
tests/test_stream.py::test_stream_record PASSED                                                           [ 21%]
tests/test_stream.py::test_stream_wait_event PASSED                                                       [ 24%]
tests/test_stream.py::test_stream_wait_invalid_event PASSED                                               [ 27%]
tests/test_stream.py::test_stream_device PASSED                                                           [ 30%]
tests/test_stream.py::test_stream_context PASSED                                                          [ 33%]
tests/test_stream.py::test_stream_from_foreign_stream PASSED                                              [ 36%]
tests/test_stream.py::test_stream_from_handle PASSED                                                      [ 39%]
tests/test_stream.py::test_legacy_default_stream PASSED                                                   [ 42%]
tests/test_stream.py::test_per_thread_default_stream PASSED                                               [ 45%]
tests/test_stream.py::test_stream_subclassing PASSED                                                      [ 48%]
tests/test_stream.py::test_stream_legacy_default_subclassing PASSED                                       [ 51%]
tests/test_stream.py::test_stream_per_thread_default_subclassing PASSED                                   [ 54%]
tests/test_stream.py::test_stream_legacy_default_public_api PASSED                                        [ 57%]
tests/test_stream.py::test_stream_per_thread_default_public_api PASSED                                    [ 60%]
tests/test_stream.py::test_stream_equality_same_handle PASSED                                             [ 63%]
tests/test_stream.py::test_stream_inequality_different_handles PASSED                                     [ 66%]
tests/test_stream.py::test_stream_equality_reflexive PASSED                                               [ 69%]
tests/test_stream.py::test_stream_equality_symmetric PASSED                                               [ 72%]
tests/test_stream.py::test_stream_type_safety PASSED                                                      [ 75%]
tests/test_stream.py::test_stream_not_equal_operator PASSED                                               [ 78%]
tests/test_stream.py::test_stream_hash_consistency PASSED                                                 [ 81%]
tests/test_stream.py::test_stream_hash_equality_same_handle PASSED                                        [ 84%]
tests/test_stream.py::test_stream_hash_inequality_different_handles PASSED                                [ 87%]
tests/test_stream.py::test_stream_dict_key PASSED                                                         [ 90%]
tests/test_stream.py::test_stream_set_membership PASSED                                                   [ 93%]
tests/test_stream.py::test_builtin_stream_hash PASSED                                                     [ 96%]
tests/test_stream.py::test_default_stream_consistency PASSED                                              [100%]

============================================== 33 passed in 0.37s ===============================================

Note

Pre-commit's mypy-pathfinder check fails on load_dl_linux.py, but this is a pre-existing issue in cuda_pathfinder unrelated to these cuda_core changes.

Fixes #1445

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