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Refactor decimal casting in arrow-cast to converge on the same rescale logic used by the parquet variant cast

Describe the solution you'd like

Originally post by @scovich in #8552 (comment)

• rework convert_to_smaller_scale_decimal and convert_to_bigger_or_equal_scale_decimal

  • no longer take array or cast_options as input
  • return Ok((f, is_infallible_cast) which corresponds to the return type Result<(impl Fn(I::Native) -> Option<O::Native>, bool), ArrowError>

• define a new generic apply_decimal_cast function helper

  • it takes as input array, cast_options and the (impl Fn, bool) pair produced by a convert_to_xxx_scale_decimal helper
  • it handles the three ways of applying f to an array

• rework cast_decimal_to_decimal and cast_decimal_to_decimal_same_type to call those functions (see below)

• rescale_decimal would be the single-row equivalent of cast_decimal_to_decimal, returning Option<O::Native>

• The decimal builder's constructor calls validate_decimal_precision_and_scale and fails on error, so we don't need to validate on a per-row basis.

cast_decimal_to_decimal

let array: PrimitiveArray<O> = if input_scale > output_scale {
    let (f, is_infallible_cast) = convert_to_smaller_scale_decimal(...)?;
    apply_decimal_cast(array, cast_options, f, is_infallible)?
} else {
    let (f, is_infallible_cast) = convert_to_bigger_or_equal_scale_decimal(...)?;
    apply_decimal_cast(array, cast_options, f, is_infallible)?
}

rescale_decimal

if input_scale > output_scale {
    let (f, _) = convert_to_smaller_scale_decimal(...)?;
    f(integer)
} else {
    let (f, _) = convert_to_bigger_or_equal_scale_decimal(...)?;
    f(integer)
}

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