Add optimisations

[alisha17]

1. Cached Intl.NumberFormat instances (format.ts)

• Added a formatterCache map keyed by serialized options
• Replaced all 8 new Intl.NumberFormat() / .toLocaleString() call sites with cachedFormatter()
• Updated DataTable.tsx to use formatChartKitNumber instead of inline toLocaleString
• Formatters are now created once per unique config and reused across all subsequent calls

3. Shared useChartSeries hook

• Created useChartSeries.ts with the row-pivoting logic wrapped in useMemo
• BarChart and LineChart now import useChartSeries instead of duplicating ~40 lines each
• The pivot result is memoized on the actual field props + rows reference

4. Removed redundant registerDataSources in db-manager.ts

• createDuckDbRuntime already calls registerDataSources internally with the initial sources
• Removed the second identical call that was iterating + JSON-serializing every source for nothing on new runtimes