[datafusion-spark] Support 2-argument ceil(value, scale)

[diegoQuinas]

Which issue does this PR close?

Closes #21560

Rationale for this change

The Spark ceil function supports an optional scale parameter that controls
the decimal position to round up to. This was not yet implemented in
datafusion-spark.

What changes are included in this PR?

• Updated Signature to accept 1 or 2 arguments, following the same pattern as SparkRound
• Updated return_type: floats preserve their type when a scale is provided (instead of returning Int64); scale=0 preserves the original behavior
• Added get_scale() helper to extract the optional scale argument, returning None for NULL scale (which produces a NULL result)
• Added ceil_float() helper for ceiling floats at arbitrary decimal positions
• Updated spark_ceil_scalar and spark_ceil_array to apply the scale

Are these changes tested?

Yes, unit tests covering:

• Float64/Float32 scalar with positive scale, negative scale, zero scale, and NULL scale
• Float64 array with scale
• Existing 1-argument tests continue to pass

Are there any user-facing changes?

Yes — ceil(expr, scale) is now supported in addition to the existing ceil(expr).