refactor: 🚚 rename to extensions.py from custom_checks.py (#158)

# Description

As per #156, renaming custom checks to be extensions instead. Will
implement the Extensions class in another PR.

Needs a quick review.

## Checklist

- [x] Ran `just run-all`

Author: lwjohnst86

src/check_datapackage/__init__.py

@@ -2,13 +2,13 @@
 
 from .check import check
 from .config import Config
-from .custom_check import CustomCheck, Extensions, RequiredCheck
 from .examples import (
     example_field_properties,
     example_package_properties,
     example_resource_properties,
 )
 from .exclusion import Exclusion
+from .extensions import CustomCheck, Extensions, RequiredCheck
 from .issue import Issue
 from .read_json import read_json
 

src/check_datapackage/check.py

@@ -7,8 +7,8 @@
 
 from check_datapackage.config import Config
 from check_datapackage.constants import DATA_PACKAGE_SCHEMA_PATH, GROUP_ERRORS
-from check_datapackage.custom_check import apply_extensions
 from check_datapackage.exclusion import exclude
+from check_datapackage.extensions import apply_extensions
 from check_datapackage.internals import (
     _filter,
     _flat_map,

src/check_datapackage/config.py

@@ -1,8 +1,8 @@
 from dataclasses import dataclass, field
 from typing import Literal
 
-from check_datapackage.custom_check import Extensions
 from check_datapackage.exclusion import Exclusion
+from check_datapackage.extensions import Extensions
 
 
 @dataclass

src/check_datapackage/custom_check.py renamed to src/check_datapackage/extensions.py

@@ -4,13 +4,13 @@
 
 from check_datapackage.check import check
 from check_datapackage.config import Config
-from check_datapackage.custom_check import Extensions
 from check_datapackage.examples import (
     example_package_properties,
     example_resource_properties,
 )
 from check_datapackage.exclusion import Exclusion
-from tests.test_custom_check import lowercase_check
+from check_datapackage.extensions import Extensions
+from tests.test_extensions import lowercase_check
 
 # "MUST" checks
 

tests/test_check.py

@@ -1,10 +1,10 @@
 from check_datapackage.check import check
 from check_datapackage.config import Config
-from check_datapackage.custom_check import CustomCheck, Extensions, RequiredCheck
 from check_datapackage.examples import (
     example_package_properties,
     example_resource_properties,
 )
+from check_datapackage.extensions import CustomCheck, Extensions, RequiredCheck
 from check_datapackage.issue import Issue
 
 lowercase_check = CustomCheck(