[VL] GlutenCSVLegacyTimeParserSuite legacy Timestamp mode is not supported

### Backend

VL (Velox)

### Bug description

// Unsupported format: yyyy-MM-dd HH:mm:ss.SSS
```
2026-01-22T09:15:29.4117826Z - Write timestamps correctly in ISO8601 format by default *** FAILED ***
2026-01-22T09:15:29.4118820Z Results do not match for query:
2026-01-22T09:15:29.4121572Z Timezone: sun.util.calendar.ZoneInfo[id="America/Los_Angeles",offset=-28800000,dstSavings=3600000,useDaylight=true,transitions=185,lastRule=java.util.SimpleTimeZone[id=America/Los_Angeles,offset=-28800000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]]
2026-01-22T09:15:29.4124474Z Timezone Env:
2026-01-22T09:15:29.4124883Z
2026-01-22T09:15:29.4125269Z == Parsed Logical Plan ==
2026-01-22T09:15:29.4125946Z UnresolvedDataSource format: csv, isStreaming: false, paths: 1 provided
2026-01-22T09:15:29.4126636Z
2026-01-22T09:15:29.4127042Z == Analyzed Logical Plan ==
2026-01-22T09:15:29.4127508Z date: string
2026-01-22T09:15:29.4127952Z Relation [date#23116] csv
2026-01-22T09:15:29.4128393Z
2026-01-22T09:15:29.4128803Z == Optimized Logical Plan ==
2026-01-22T09:15:29.4129380Z Relation [date#23116] csv
2026-01-22T09:15:29.4129752Z
2026-01-22T09:15:29.4129996Z == Physical Plan ==
2026-01-22T09:15:29.4131626Z FileScan csv [date#23116] Batched: false, DataFilters: [], Format: CSV, Location: InMemoryFileIndex(1 paths)[file:/tmp/spark-4339fa22-4a66-46b0-a8e1-535b6d2bfbcd/iso8601timestamps..., PartitionFilters: [], PushedFilters: [], ReadSchema: struct
2026-01-22T09:15:29.4133503Z
2026-01-22T09:15:29.4133787Z == Results ==
2026-01-22T09:15:29.4134095Z
2026-01-22T09:15:29.4134350Z == Results ==
2026-01-22T09:15:29.4134765Z !== Correct Answer - 5 == == Spark Answer - 5 ==
2026-01-22T09:15:29.4135354Z !struct<> struct
2026-01-22T09:15:29.4135898Z ![1800-01-01T10:07:02.000-07:52:58] [01/01/1800 18:00Z]
2026-01-22T09:15:29.4136432Z ![1885-01-01T10:30:00.000-08:00] [01/01/1885 18:30Z]
2026-01-22T09:15:29.4136922Z ![2014-10-27T18:30:00.000-07:00] [26/08/2015 18:00]
2026-01-22T09:15:29.4137434Z ![2015-08-26T18:00:00.000-07:00] [27/10/2014 18:30]
2026-01-22T09:15:29.4138037Z ![2016-01-28T20:00:00.000-08:00] [28/01/2016 20:00] (QueryTest.scala:273)
```

```
2026-01-22T09:16:00.9069041Z - csv with variant *** FAILED ***
2026-01-22T09:16:00.9069591Z Results do not match for query:
2026-01-22T09:16:00.9072913Z Timezone: sun.util.calendar.ZoneInfo[id="America/Los_Angeles",offset=-28800000,dstSavings=3600000,useDaylight=true,transitions=185,lastRule=java.util.SimpleTimeZone[id=America/Los_Angeles,offset=-28800000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]]
2026-01-22T09:16:00.9075775Z Timezone Env:
2026-01-22T09:16:00.9076098Z
2026-01-22T09:16:00.9076380Z == Parsed Logical Plan ==
2026-01-22T09:16:00.9076829Z 'Project [unresolvedalias(cast('v as string))]
2026-01-22T09:16:00.9077337Z +- Relation [v#30332] csv
2026-01-22T09:16:00.9077706Z
2026-01-22T09:16:00.9078003Z == Analyzed Logical Plan ==
2026-01-22T09:16:00.9078383Z v: string
2026-01-22T09:16:00.9078726Z Project [cast(v#30332 as string) AS v#30333]
2026-01-22T09:16:00.9079198Z +- Relation [v#30332] csv
2026-01-22T09:16:00.9079545Z
2026-01-22T09:16:00.9079842Z == Optimized Logical Plan ==
2026-01-22T09:16:00.9080314Z Project [cast(v#30332 as string) AS v#30333]
2026-01-22T09:16:00.9080799Z +- Relation [v#30332] csv
2026-01-22T09:16:00.9081156Z
2026-01-22T09:16:00.9081430Z == Physical Plan ==
2026-01-22T09:16:00.9081867Z *(1) Project [cast(v#30332 as string) AS v#30333]
2026-01-22T09:16:00.9083780Z +- FileScan csv [v#30332] Batched: false, DataFilters: [], Format: CSV, Location: InMemoryFileIndex(1 paths)[file:/tmp/spark-e0f3df4e-41e5-468b-a044-8748de0bdfd6], PartitionFilters: [], PushedFilters: [], ReadSchema: struct
2026-01-22T09:16:00.9085414Z
2026-01-22T09:16:00.9085698Z == Results ==
2026-01-22T09:16:00.9086012Z
2026-01-22T09:16:00.9086285Z == Results ==
2026-01-22T09:16:00.9086783Z !== Correct Answer - 6 == == Spark Answer - 6 ==
2026-01-22T09:16:00.9087522Z !struct<> struct
2026-01-22T09:16:00.9088314Z ![{"_c0":"2000-01-01","_c1":"2000-01-01 01:02:03+00:00"}] [{"_c0":"2000-01-01","_c1":"2000-01-01 01:02:03"}]
2026-01-22T09:16:00.9089409Z [{"_c0":"field 1","_c1":"field2"}] [{"_c0":"field 1","_c1":"field2"}]
2026-01-22T09:16:00.9090142Z [{"_c0":"missing"}] [{"_c0":"missing"}]
2026-01-22T09:16:00.9090904Z [{"_c0":100,"_c1":1.1}] [{"_c0":100,"_c1":1.1}]
2026-01-22T09:16:00.9091709Z [{"_c0":1000000000,"_c1":"hello","_c2":"extra"}] [{"_c0":1000000000,"_c1":"hello","_c2":"extra"}]
2026-01-22T09:16:00.9092851Z [{"_c0":null,"_c1":true}] [{"_c0":null,"_c1":true}] (QueryTest.scala:273)
```

### Gluten version

_No response_

### Spark version

None

### Spark configurations

_No response_

### System information

_No response_

### Relevant logs

```bash

```

The failures are reported at QueryTest.scala:273; start by locating GlutenCSVLegacyTimeParserSuite and its legacy Timestamp-mode test cases. Reproduce the two CSV query failures, then use the expected-versus-actual results to verify that legacy timestamp parsing and variant output match the stated expectations.

Written by the indexing model from the issue text.