[mypy-fix] Type fixes for graham_scan

[spazm]

Describe your change:

Fixed type annoations on other/graham_scan

Before

% git checkout master
% mypy --ignore-missing-imports  graham_scan.py
graham_scan.py:17: error: "list" expects 1 type argument, but 2 given
graham_scan.py:60: error: "list" expects 1 type argument, but 2 given
graham_scan.py:88: error: Argument 2 to "insert" of "list" has incompatible type "Tuple[int, int]"; expected "List[Any]"
graham_scan.py:97: error: Missing return statement
graham_scan.py:98: error: "list" expects 1 type argument, but 2 given
graham_scan.py:140: error: Need type annotation for "stack"
Found 6 errors in 1 file (checked 1 source file)

After

% git checkout mypy-fix-other-graham_scan
% mypy --ignore-missing-imports  graham_scan.py
Success: no issues found in 1 source file

% mypy --ignore-missing-imports  --strict graham_scan.py
Success: no issues found in 1 source file

• 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}.

[cclauss]

LGTM. Thanks for doing this!