perf(ui): speed up experiment runs page with many metrics/params

[vikranth-t]

• Virtualize the runs sort-selector dropdown so only visible options are mounted, eliminating the tab freeze when opening sort on experiments with thousands of metrics/params (full list still available; no cap).
• Reset the cumulative column-key caches when switching experiments to fix unbounded growth and stale columns leaking across experiments (which could also wrongly trip the large-column-count threshold); anti-flicker behavior within an experiment is preserved.
• Memoize getVisibleTagKeyList in ExperimentViewRunsControls (an O(runs*tags) scan) so it no longer re-runs on every render, matching the other call sites.

Related Issues/PRs

Closes | Relates to #issue_number

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