Extend `CastUtils.java` with helpers for `byte` and `short` ANSI cast
targets and use them from `Cast.scala`. Drops the byte/short-target
dispatch (and the now-unused `lowerAndUpperBound` Scala helper) added
in SPARK-56909 -- after this PR, all integral and fractional narrowing
ANSI casts share the same `CastUtils.<...>Exact` one-line codegen.

Helpers added:
* `shortToByteExact(short)`, `intToByteExact(int)`, `longToByteExact(long)`
* `intToShortExact(int)`, `longToShortExact(long)`
* `floatToByteExact(float)`, `doubleToByteExact(double)`
* `floatToShortExact(float)`, `doubleToShortExact(double)`

`Cast.scala` changes:
* `castIntegralTypeToIntegralTypeExactCode` / `castFractionToIntegralTypeCode`
  no longer dispatch on target type -- the helper-name pattern
  `${integralPrefix(from)}To${target.capitalize}Exact` covers all four
  target types.
* Eval paths for `castToByte` and `castToShort` add ANSI cases for
  `ShortType` / `IntegerType` / `LongType` / `FloatType` / `DoubleType`
  source types that delegate to the new helpers; the existing
  `exactNumeric.toInt(b) + bounds-check` fallback now only handles the
  remaining `Decimal` source.

Part of SPARK-56908 (umbrella). The original byte/short ANSI cast bodies
were 5 lines each across 8 call sites; this PR collapses them to one
line per call site, matching the int/long target work from SPARK-56909.

No. The compiled behavior is identical; only the emitted Java source
text changes.

```
build/sbt "catalyst/testOnly *CastSuite *CastWithAnsiOnSuite \
  *CastWithAnsiOffSuite *AnsiCastSuite *TryCastSuite \
  *ExpressionClassIdentitySuite"
```

312/312 pass.

Generated-by: Cursor 1.x

### What changes were proposed in this pull request?

Extend `CastUtils.java` with two helpers for decimal precision adjustment
and use them from `Cast.changePrecision` (both the eval and codegen
implementations). The new helpers mutate the input `Decimal` in place
(matching the behavior of the existing inline codegen), so they're safe
to call on the temporary produced by `Decimal.fromString(...)` /
`Decimal.apply(...)` / decimal-arithmetic results.

Helpers added:
* `changePrecisionExact(Decimal, int, int, QueryContext)`: ANSI throw on
  overflow, preserves the per-call-site `QueryContext` so error messages
  keep their query-origin info.
* `changePrecisionOrNull(Decimal, int, int)`: non-ANSI, returns `null`
  on overflow (no `QueryContext` needed).

`Cast.scala` changes:
* `changePrecision` eval method dispatches on `nullOnOverflow` and
  delegates to the appropriate helper.
* `changePrecision` codegen method has three branches now: the existing
  `canNullSafeCast` fast path (unchanged), a `nullOnOverflow` branch
  (inline), and the ANSI throw branch which now emits a one-line
  `CastUtils.changePrecisionExact(...)` call instead of the 5-line
  `if/else` overflow block.

### Why are the changes needed?

Part of SPARK-56908 (umbrella). The ANSI throw branch of
`Cast.changePrecision` is hit by every cast to decimal that may overflow
(very common in TPC-DS, where `cast(int as decimal(7,2))` is widespread).
Collapsing the 5-line inline body to one line shrinks the generated
Java source for those plans.

### Does this PR introduce _any_ user-facing change?

No. The compiled behavior is identical; only the emitted Java source
text changes.

### How was this patch tested?

```
build/sbt "catalyst/testOnly *CastSuite *CastWithAnsiOnSuite \
  *CastWithAnsiOffSuite *AnsiCastSuite *TryCastSuite *DecimalSuite \
  *ExpressionClassIdentitySuite"
```

337/337 pass.

### Was this patch authored or co-authored using generative AI tooling?

Generated-by: Cursor 1.x

### What changes were proposed in this pull request?

Use `CastUtils.changePrecisionExact` / `changePrecisionOrNull` (added in
SPARK-56911) from the `DecimalType.Fixed` branches of:
* `BinaryArithmetic.doGenCode` (covers `Add` / `Subtract` / `Multiply`
  on `Decimal`).
* `BinaryDivModLike.doGenCode` (covers `Divide` / `IntegralDivide` /
  `Remainder` / `Pmod` on `Decimal`).
* `BinaryArithmetic.checkDecimalOverflow` (eval path used by both
  groups via `numeric.plus`/`minus`/`times`/`div`).

Each call site goes from
`eval1.$op(eval2).toPrecision(p, s, ROUND_HALF_UP, !failOnError, ctx)`
+ a 4-line null check to a single
`CastUtils.changePrecision{Exact,OrNull}` call.

### Why are the changes needed?

Part of SPARK-56908 (umbrella). Decimal arithmetic is widespread in
TPC-DS plans, and the `BinaryArithmetic` Decimal branch was one of the
longer ANSI codegen bodies still emitted inline.

### Does this PR introduce _any_ user-facing change?

No. The compiled behavior is identical; only the emitted Java source
text changes.

### How was this patch tested?

```
build/sbt "catalyst/testOnly *ArithmeticExpressionSuite *DecimalSuite"
```

60/60 pass.

### Was this patch authored or co-authored using generative AI tooling?

Generated-by: Cursor 1.x