Excel export issue

[NamanMahor]

when data is exported to the Excel XLSX format from Pivot table views in Rill, two issues arise:

1. Time dimension fields appears as strings such as 2025-01-23T00:00:00Z

Actually it occurs when we export to csv so need fix in csv export(confirm from file share by Customer).

2. Other values appear with quotation marks surrounding them

This was issue in both excel csv and parquet export. This issue was happening when we convert to parquet file in case of pivot table.

Closed #6765

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[k-anshul]

nit: this format is auto converted to datetime in excel

[k-anshul]

Datetype date will not be scanned to a string.

h, err := drivers.Open("clickhouse", "default", map[string]any{"dsn": "clickhouse://localhost:9000"}, storage.MustNew(os.TempDir(), nil), activity.NewNoopClient(), zap.NewNop())
	if err != nil {
		panic(err)
	}

	olap, _ := h.AsOLAP("default")

	result, err := olap.Execute(context.Background(), &drivers.Statement{
		Query: "SELECT '2024-01-01'::Date32",
	})
	if err != nil {
		panic(err)
	}
	var t any
	for result.Next() {
		if err := result.Scan(&t); err != nil {
			panic(err)
		}
		// panic: interface conversion: interface {} is time.Time, not string
		println(t.(string))
	}