fix: log as method gives symbolic output for non positive base

[devansh-srv]

This pull request updates the behaviour of the log method in the Integer class to handle cases where the base is non-positive to give symbolic output and added tests for the same. This solves the issue #39959
like this

sage: 8.log(-2)
3*log(2)/(I*pi + log(2))

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

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