chore: Replace general Ruff F401 exclusion with per-file-ignore

A general problem with F401 is __init__.py because naturally symbols
imported there merely define the package interface and aren't actually
used/referenced apart from the import.

Basically there are two ways to go about this:

1. Define __all__ in __init__.py
(see [Importing * From a Package](https://docs.python.org/3/tutorial/modules.html#importing-from-a-package))

or

2. Add __init__.py to Ruff's per-file-ignores
(see [Ruff per-file-ignores](https://docs.astral.sh/ruff/settings/#per-file-ignores)).

Adding __init__.py to per-file-ignores imo is a better option here
because __all__ encourages the 'from <package> import *' antipattern.

Closes: #34

pyproject.toml

@@ -24,9 +24,8 @@ hypothesis = "^6.108.4"
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
 
-
-[tool.ruff]
-lint.ignore = ["F401"]
+[tool.ruff.lint.per-file-ignores]
+"__init__.py" = ["F401"]
 
 [tool.deptry.package_module_name_map]
 sparqlwrapper = "SPARQLWrapper"