Add the ruff INP001 rule

This check that every directory with a python file has a __init__.py
Ignore directories outside the mantidimaging package, as these have some standalone files

pyproject.toml

@@ -3,10 +3,13 @@ line-length = 120
 target-version = "py310"
 
 [tool.ruff.lint]
-select = ["F", "E", "W", "UP", "B", "C4", "FA", "NPY"]
+select = ["F", "E", "W", "UP", "B", "C4", "FA", "NPY", "INP"]
 fixable = ["UP"]
 ignore = ["UP014"]
 
+[tool.ruff.lint.per-file-ignores]
+"!mantidimaging/**.py" = ["INP"]
+
 [tool.pyright]
 typeCheckingMode = "basic"
 reportMissingImports = false