More CI cleanup, add style workflow (#107)

- Changes on the `test.yml` workflow:
  - Using poetry instead of pip. Contrary to what I wrote in #75, it is possible to use poetry (and have the benefits of shorter install times) without the need for having two separate versions of `pyproject.toml` and `poetry.lock`.
  - Reduce the trigger scope to only run when files in these directories are modified:
    - `lerobot/`
    - `tests/`
    - `examples/`
    - `.github/`
- Add `style.yml` workflow for doing a `ruff check` pass on the code
- More cleanup (removed deprecated workflow)

tests/test_examples.py

@@ -1,5 +1,6 @@
 # TODO(aliberts): Mute logging for these tests
 import subprocess
+import sys
 from pathlib import Path
 
 
@@ -11,7 +12,7 @@ def _find_and_replace(text: str, finds_and_replaces: list[tuple[str, str]]) -> s
 
 
 def _run_script(path):
-    subprocess.run(["python", path], check=True)
+    subprocess.run([sys.executable, path], check=True)
 
 
 def test_example_1():