Add url and typing hint for BFS

[asukaminato0721]

Describe your change:

Add typing for bfs and make the code more brief.

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

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• 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.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• 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.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

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[asukaminato0721]

Fix several hidden troubles.

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[asukaminato0721]

Fix the type of return value of bfs.

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[cclauss]

You will need to change all instances of bfs() to breadth_first_search().

[asukaminato0721]

Change all instances of bfs() to breadth_first_search().

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[asukaminato0721]

Change the function name in annotate.

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[asukaminato0721]

Add one more blank line.

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[asukaminato0721]

Delete one blank line.

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[cclauss]

Do not worry about Euler 47

[asukaminato0721]

Delete one blank line.
Confused with this https://www.flake8rules.com/rules/W391.html

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[cclauss]

We already have a breadth_first_search.py. Should this file be deleted??

[asukaminato0721]

There are two different dfs files.
https://github.com/TheAlgorithms/Python/blob/master/graphs/depth_first_search.py
https://github.com/TheAlgorithms/Python/blob/master/graphs/depth_first_search_2.py
The same as these two bfs files.
https://github.com/TheAlgorithms/Python/blob/master/graphs/bfs.py
https://github.com/TheAlgorithms/Python/blob/master/graphs/breadth_first_search.py

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