update dependencies before build (#91)

Old implementation has used add step in order to fetch dependencies,
which could lead to build errors in case if dependency list was updated.

New solution uses dependencies which are declared at current version and
fetch them (if required and if enabled) before update process.

Closes #90

tests/ahriman/models/test_package.py

@@ -125,6 +125,14 @@ def test_licenses(package_ahriman: Package) -> None:
     assert sorted(package_ahriman.licenses) == package_ahriman.licenses
 
 
+def test_packages_full(package_ahriman: Package) -> None:
+    """
+    must return full list of packages including provides
+    """
+    package_ahriman.packages[package_ahriman.base].provides = [f"{package_ahriman.base}-git"]
+    assert package_ahriman.packages_full == [package_ahriman.base, f"{package_ahriman.base}-git"]
+
+
 def test_from_archive(package_ahriman: Package, pyalpm_handle: MagicMock, mocker: MockerFixture) -> None:
     """
     must construct package from alpm library