Update workunit history page to handle missing cost and improve comparison/averages

[sodon-lnr]

Update workunit history details page functionality

On the previous runs tab of the workunit history details component:

• If the cluster does not provide cost data, show runtime history instead, ensuring the page remains informative even when cost info is unavailable.
• Add new average cost metrics for failures and successes separately, but keep displaying the overall average cost as well.
• Ensure the 'vs Previous' column computes the difference correctly — currently, it is not accurate every time. Fix its comparison logic so it consistently shows accurate changes relative to the previous valid row.
  • It should also show the vs previous value for cost if there is cost data or runtime if there is no cost data

Acceptance Criteria:

• Runtime history displays automatically if cost info is missing.
• Both 'average cost (success)' and 'average cost (failure)' are shown, alongside an 'overall average cost'.
• The 'vs Previous' column reflects correct cost and runtime comparisons for all cases.
• Add or update relevant tests and documentation.