Use base classes to simplify issue finders and dependency getter

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Simplify issue finders and dependency getter logic by using base classes in order to reduce duplication and respect a common format.
Commit by commit review is advised here.

[codecov-commenter]

Codecov Report

Merging #154 (bfed0f5) into main (1b12183) will increase coverage by 0.3%.
The diff coverage is 90.9%.

@@           Coverage Diff           @@
##            main    #154     +/-   ##
=======================================
+ Coverage   92.9%   93.2%   +0.3%     
=======================================
  Files         43      45      +2     
  Lines       1355    1369     +14     
=======================================
+ Hits        1259    1277     +18     
+ Misses        96      92      -4     

Impacted Files	Coverage Δ
deptry/issues_finder/misplaced_dev.py	29.4% <41.6%> (ø)
deptry/core.py	58.3% <50.0%> (+1.1%)	⬆️
deptry/issues_finder/transitive.py	91.6% <83.3%> (ø)
deptry/issues_finder/base.py	92.3% <92.3%> (ø)
deptry/dependency_getter/base.py	95.0% <95.0%> (ø)
deptry/dependency_getter/poetry.py	100.0% <100.0%> (ø)
deptry/dependency_getter/requirements_txt.py	97.4% <100.0%> (+0.8%)	⬆️
deptry/issues_finder/missing.py	100.0% <100.0%> (ø)
deptry/issues_finder/obsolete.py	96.5% <100.0%> (ø)
tests/dependency_getter/test_poetry.py	100.0% <100.0%> (ø)
... and 4 more

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[fpgmaas]

Looks good to me! Merge requests that manage to remove more lines than that they add are the best 😄 Having to pass dev_dependencies to some issue_finders is an artifact of before I added the is_dev_dependency flag to Module. Maybe it would be good to add a unit test for MisplacedDevDependencyFinder, now that we are making some refactoring changes in it, e.g.

tests/issues_finder/misplaced_dev.py

from deptry.issues_finder.misplaced_dev import MisplacedDevDependenciesFinder
from deptry.module import Module


def test_simple():
    dependencies = ["bar"]
    dev_dependencies=["foo"]
    modules = [Module("foo", dev_top_levels=["foo"], is_dev_dependency=True)]
    deps = MisplacedDevDependenciesFinder(imported_modules=modules, dependencies=dependencies, dev_dependencies=dev_dependencies).find()
    assert len(deps) == 1
    assert deps[0] == "foo"