[SPARK-53554] Fix sum_distinct

[sarutak]

What changes were proposed in this pull request?

This PR aims to fix sum_distinct.
In the current spark-connect-rust, sum_distinct doesn't work correctly.
If we run the following code,

let df = spark
    .sql("SELECT * FROM VALUES (1), (2), (3), (1), (2), (3) AS data(value)")
    .await?;
df.select([sum_distinct(col("value")).alias("sum")])
    .show(None, None, None)
    .await?;

We will get the following error.

Error: AnalysisException("[UNRESOLVED_ROUTINE] Cannot resolve routine `sum_distinct` on search path [`system`.`builtin`, `system`.`session`, `spark_catalog`.`default`]. SQLSTATE: 42883")

Why are the changes needed?

Bug fix.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Added new tests.

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

No.

[sarutak]

@viirya Could you help review this if possible? Thanks.

[sarutak]

@viirya Thank you for taking a look at this PR!

[sarutak]

This PR has already approved and the last change is just inserting blank lines.
I'll merge this into master
Thank you for the review, @viirya !