Move dev dependencies into a PEP 735 dependency group

Replaces requirements_dev.txt with a [dependency-groups] dev table in
pyproject.toml, and updates CI to install via `pip install --group dev`.

Author: ndevenish

.github/workflows/python.yml

@@ -41,7 +41,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements_dev.txt dist/*.whl
+          pip install --group dev dist/*.whl
       - name: Test with pytest
         run: |
           pytest tests

pyproject.toml

@@ -39,6 +39,16 @@ Bug-Tracker = "https://github.com/DiamondLightSource/python-workflows/issues"
 [project.optional-dependencies]
 prometheus = ["prometheus-client"]
 
+[dependency-groups]
+dev = [
+    "prometheus-client",
+    "pytest",
+    "pytest-cov",
+    "pytest-mock",
+    "pytest-timeout",
+    "websocket-client",
+]
+
 [project.entry-points."libtbx.dispatcher.script"]
 "workflows.validate_recipe" = "workflows.validate_recipe"