[ic-data-table] sortable slotted columns

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## Summary
I should be able to specify a string / number value that can be used as a sort key for a column that it has been slotted in to the data table.

- [ ] Add prop to disable sorting on a column
- [ ] Add functionality for sorting slotted content

## 💬 Description

This column is a timestamp value that has been formatted for display:



I would like to be able to sort on this in some way but currently trying to sort a slotted column does nothing

## 💰 Use value
Slotted columns are currently broken for sorting, the sort function is there and does nothing, at a minimum it should be hidden but ideally it should work

## 📝 Acceptance Criteria
If relevant, describe in full detail the different interactions and edge cases that the component or patterns needs to fulfil.

*Given*
*When*
*Then*

## ✏ Designs
If there's a Figma design file (or other mock-up), include it here.

## 🧾 Guidance
If there's written guidance or documentation, include a link to it here.

## Additional info
Tell us anything else useful to help us understand your suggestion.

The issue names the ic-data-table component but does not identify source files or tests; start by locating its existing sorting behavior and how slotted columns are represented. Clarify and cover both disabling sorting for a column and supplying a string or number sort key for slotted content, including the formatted timestamp case.

Written by the indexing model from the issue text.