Simplify imports

[bjorn-martinsson]

Currently PyRival uses a somewhat complicated import system

1. When adding/modifying a python file, you have to update the corresponding __init__.py in a kind of complicated way.
2. Every file in PyRival is imported on doing any kind of import in PyRival. This means that we can't do costly calculations on imports of a certain file, since that would slow down imports of other files.
3. The PyRival namespace is currently mixed with a lot of functions. I feel we should try to keep all of the files more separate.

I propose fixing this by just having a single __init__.py file in the pyrival package containing a modification to __path__, allowing all .py files in pyrival/... to be reachable by doing import pyrival.insert_filename_here. This greatly simplifies PyRival, while also fixing all of the 3 issues above.

With these changes it is possible to do things like

• import pyrival.convex_hull_trick
• from pyrival import convex_hull_trick
• from pyrival.convex_hull_trick import convex_hull_trick (this imports the function convex_hull_trick inside convex_hull_trick.py)
• from pyrival.convex_hull_trick import *

@Mukundan314 and @cheran-senthil what do you think about this? I think something like this would definitely be an improvement.

[bjorn-martinsson]

For some reason the automatic tests seem to break from this, but I can run things locally without any import errors. Really not sure what the issue is.

[Mukundan314]

The ordersort tests are still using the old import format.

Edit: Fixed it

[bjorn-martinsson]

The test are failing because your import syntax is wrong for the gcd test (fixed it)

I'm seeing errors like this under "tox run"

ImportError while importing test module '/home/runner/work/PyRival/PyRival/tests/algebra/test_chinese_remainder.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/algebra/test_chinese_remainder.py:3: in <module>
    from pyrival.chinese_remainder import *
E   ModuleNotFoundError: No module named 'pyrival.chinese_remainder'

I'm really not sure why I'm getting these on tox. Locally running the imports does not cause any errors.