[BUG] Cast String to Decimal could return null incorrectly when scale = precision

[thirtiseven]

Describe the bug
Cast string to decimal could return null on GPU while a valid value on CPU in some edge cases when scale - precision.

An example: -9.72792462805176E-15 will return null when cast to decimal(15,15) on GPU but -1.0E-14 on CPU.

It seems very edge.

Steps/Code to reproduce bug

scala> import org.apache.spark.sql.functions._
import org.apache.spark.sql.functions._

scala> import org.apache.spark.sql.types._
import org.apache.spark.sql.types._

scala> val data = Seq("-9.72792462805176E-15").toDF
data: org.apache.spark.sql.DataFrame = [value: string]

scala> data.write.mode("OVERWRITE").parquet("TEMP")
24/05/24 08:07:55 WARN GpuOverrides:
*Exec <DataWritingCommandExec> will run on GPU
  *Output <InsertIntoHadoopFsRelationCommand> will run on GPU
  ! <LocalTableScanExec> cannot run on GPU because GPU does not currently support the operator class org.apache.spark.sql.execution.LocalTableScanExec
    @Expression <AttributeReference> value#1 could run on GPU


scala> val df = spark.read.parquet("TEMP")
df: org.apache.spark.sql.DataFrame = [value: string]

scala> df.select(col("value").cast(DecimalType(15, 15))).show()
24/05/24 08:08:13 WARN GpuOverrides:
!Exec <CollectLimitExec> cannot run on GPU because the Exec CollectLimitExec has been disabled, and is disabled by default because Collect Limit replacement can be slower on the GPU, if huge number of rows in a batch it could help by limiting the number of rows transferred from GPU to CPU. Set spark.rapids.sql.exec.CollectLimitExec to true if you wish to enable it
  @Partitioning <SinglePartition$> could run on GPU
  *Exec <ProjectExec> will run on GPU
    *Expression <Alias> cast(cast(value#6 as decimal(15,15)) as string) AS value#12 will run on GPU
      *Expression <Cast> cast(cast(value#6 as decimal(15,15)) as string) will run on GPU
        *Expression <Cast> cast(value#6 as decimal(15,15)) will run on GPU
    *Exec <FileSourceScanExec> will run on GPU

+-----+
|value|
+-----+
| null|
+-----+


scala> spark.conf.set("spark.rapids.sql.enabled", "false")

scala> df.select(col("value").cast(DecimalType(15, 15))).show()
+--------+
|   value|
+--------+
|-1.0E-14|
+--------+

A test cases:

def test_cast_double_to_string_to_decimal():
    assert_gpu_and_cpu_are_equal_collect(
        lambda spark : unary_op_df(spark, double_gen, length=100000).selectExpr(
            "cast(cast(a as string) as decimal(15, 15))"),
            conf = {'spark.rapids.sql.castFloatToDecimal.enabled': 'true',
                    'spark.rapids.sql.castDecimalToFloat.enabled': 'true',
                    'spark.rapids.sql.castFloatToString.enabled': 'true'})

Expected behavior
CPU and GPU results should match.

Environment details (please complete the following information)
latest code, jdk 8, tested spark 330 & 341