Rename test/ to tests/ to match pytest testpaths config

[vayset]

What

Renames the test/ directory to tests/.

Why

pyproject.toml sets testpaths = ["tests"] and MANIFEST.in already includes recursive-include tests *.py, but the directory is named test/. As a result, running pytest with no arguments does not pick up the configured test path. This renames the directory to match the existing config (and the common Python convention). No file contents are changed — it is a pure rename.

Test plan

Ran pytest from the repo root on this branch: all 8 tests in tests/test_io_utils.py are collected and pass. (Tested on macOS, where the module-level triton import had to be worked around locally — that issue is tracked separately in #179 / #482.)

🤖 Generated with Claude Code

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