Fix: DO-3658: Fix Table non-unique index values, fix sorting by unnamed index

[Roman-Kornev]

Motivation and Context

• Fixed a crash in Table pagination where rows containing non-unique index values would cause a slicing error, as rows were paginated by DataFrame index instead of iloc row ordering.
• Fixed an issue in Table where sorting by an unnamed index would not work, as the default __index__ unnamed index column does not exist in the original DataFrame.

Implementation Description

Any new dependencies Introduced

How Has This Been Tested?

PR Checklist:

• I have implemented all requirements? (see JIRA, project documentation).
• I am not affecting someone else's work, If I am, they are included as a reviewer.
• I have added relevant tests (unit, integration or regression).
• I have added comments to all the bits that are hard to follow.
• I have added/updated Documentation.
• I have updated the appropriate changelog with a line for my changes.

Screenshots (if appropriate):

[patricia-causalens]

Good catch, LGTM!

[krzysztof-causalens]

LGTM