perf: Faster report exporting logic (frappe#21415)

* perf: Faster report exports to Excel

Try exporting report with 100K rows, most likely it fails or takes a really long time.

Root causes:
- visible_idx was a list, lookups are SLOW AF when lists grow to 100k+
- visible_idx check is not required when I am exporting entire report.

Test with 85,000 rows.

|         | Before | After | Improvement |
| ---     | ---    | ---   | ---         |
| Export  | 25.99  | 0.77  | ~33x faster |

frappe/desk/query_report.py

@@ -349,6 +349,13 @@ def build_xlsx_data(data, visible_idx, include_indentation, ignore_visible_idx=F
 		datetime.timedelta,
 	)
 
+	if len(visible_idx) == len(data.result):
+		# It's not possible to have same length and different content.
+		ignore_visible_idx = True
+	else:
+		# Note: converted for faster lookups
+		visible_idx = set(visible_idx)
+
 	result = [[]]
 	column_widths = []