fix: Add missing flake8 and pytest dependencies to dev requirements

- Add flake8>=6.0.0 to dev dependencies (was missing, causing CI failure)
- Add pytest-cov and pytest-xdist for complete test coverage support
- Ensures all CI tools are properly installed via pip install -e .[dev]
- This should resolve the 'flake8: command not found' error

Author: jonobg

implementations/python/pyproject.toml

@@ -30,7 +30,10 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
     "pytest>=7.4.3",
+    "pytest-cov>=4.1.0",
+    "pytest-xdist>=3.3.1",
     "black>=22.12.0", 
+    "flake8>=6.0.0",
     "mypy>=1.1.1",
     "types-PyYAML>=6.0.0",
     "pylint>=2.17.4",