[ZhuchkaTriplesix]

Closes #1548.

Before (measured)

CompactResultDataset.fromRawRows decides each column's kind (int64 / float64 / string / generic). With a cell formatter (every SQL driver passes one), it called the formatter and toString() again on every non-null cell of every column that stayed uniform. A normal table, where most columns are uniform, therefore formatted every cell once just to pick the kind.

The detection loop copied as is into a standalone Dart AOT script, PostgreSQL-like formatter (is chain + toString), 6 int + 4 double + 10 string columns:

rows	before	after
5,000 (the default result cap, every query run)	3.5 ms	0.5 ms
50,000	46 ms	20 ms

Change

• The first 60 non-null cells of a column go through the formatter, as before; the rest are only type-tested (is int / is num / is String).
• This relies on the formatters printing a column's ints, numbers and strings by the column's type, not by the value. I checked all three:
  • PostgreSQL: bytea / undecoded types;
  • MySQL: binary and tinyint(1) booleans;
  • SQLite: blobs.
    So the samples show whether the column prints as its values do. A type that is not uniform is still caught on every row by the type test.
• The loop stops as soon as all three flags are false (the column can only be generic). Before, it waited for 60 samples; the result is the same.

Packing (the other ~39 ms of the 50k case in the issue) is unchanged.

Checked

Same kinds from the old and the new loop on the 50,000-row table plus:

• a column of ints broken by a string at row 40,000 → generic;
• an all-NULL column → string;
• a bytea-typed column of strings → generic.

Tests (compact_result_dataset_test.dart)

• Kinds with a formatter, with an upper bound on formatter calls during detection.
• A late value of another type still makes the column generic and keeps its text.

Not run with flutter test locally; CI decides.