Add injection support

[FlickerSoul]

• support injecting supporting files by --inject <file_path>, or injecting a buntch of .py files in a folder by --inject-all <folder_path>
• support auto injecting files in aga_injection directory sitting in cwd or any parent folders of cwd by --auto-inject
• add __call__ method to problems so that they behave like the old functions

usage

cli command

aga gen problem.py --inject ./supporting.py

supporting.py

def prize_fn(*args, **kwargs):
    pass

problem.py

from aga import problem, prize, test_case
from aga.injection import prize_fn  # the prize_fn in the supporting will be injected 

@test_case(1, aga_expect=1)
@prize(prize_fn)  # and can be used here
@problem()
def test(a: int) -> int:
    return a * a

assert test(10) == 100

[FlickerSoul]

will add tests later

[FlickerSoul]

Should be ready :)