Add DocTests to is_palindrome.py

[SaiHarshaK]

Describe your change:

This PR adds DocTests to the functions in is_palindrome.py to increase its codecoverage from 0% to 96%.
Tested this change locally and can verify that they are passing.

Ref #9943

• 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 include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[cclauss]

PEP8 discourages backslash line termination in Python because any whitespace to the right of the backslash breaks the script on a change that is invisible to the reader. Also, backslashes are not required inside of (), [], {}...

Suggested change

	>>> is_palindrome_dict(\
	ListNode(\
	1, ListNode(2, ListNode(1, ListNode(3, ListNode(2, ListNode(1)))))))
	>>> is_palindrome_dict(
	... ListNode(
	... 1, ListNode(2, ListNode(1, ListNode(3, ListNode(2, ListNode(1)))))
	... )
	... )

[SaiHarshaK]

Ruff complains that the length of the line is >88 which is why I had to split them into multiple lines.

If i do not add backslash, DocTest assumes ListNode( is the expected value and thereby the test fails

[cclauss]

You needed the three dots at the beginning of each continued line as discussed in the doctest docs.

[cclauss]

mypy takes some time to get used to but it is quite helpful in the end. If you do new_variable = None then it wants you to declare the datatype of new_variable because it refuses to guess.

[SaiHarshaK]

@cclauss Please check now

[SaiHarshaK]

Could you check the comment regarding backslashes?

[cclauss]

I changed the title from doctests to type hints but this looks good to go... Thanks.