Unify `O(sqrt(N))` `is_prime` functions under `project_euler`

[ngiachou]

Describe your change:

I changed the implementation of is_prime functions inside project_euler in order to have a unified implementation. There are some cases where the solution uses the Eratosthenes' sieve method. In some cases there is no specific gain from using that method so I changed it to the O(sqrt(n)) algorithm, but in other cases the sieve method is used in the core structure of the solution, hence I did not touch those.

• [ ] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [ ] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [ ] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• [x] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

fixes #5434

[ngiachou]

I think it is better to remove the assertion in all together since it doesn't have actual value for the implementation of the primality test algorithm and maybe it is a bit of confusing even. Should I do that? @poyea

Edit: For example in project_euler/problem_003/sol1.py lines 41-43.

[poyea]

@elpaxoudis Yeah, I think they can be removed, and the negative / type check can be performed when processing input (if any). If we want to handle the negative / type check in the function, I think it makes sense to raise an exception / an assertion failure, instead of return False.

[ngiachou]

@poyea Is there any other changes I should make?