feat(udf): support implicit cast for UDF arguments

[KveinAxel]

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What's changed and what's your intention?

This PR resolves #9998. udf functions now support implicit cast.

dev=> select decimal_add(1, 2);
- ERROR:  Failed to run the query
- 
- Caused by these errors (recent errors listed first):
-   1: Failed to bind expression: decimal_add(1, 2)
-   2: Feature is not yet implemented: unsupported function: "decimal_add"
- Tracking issue: https://github.com/risingwavelabs/risingwave/issues/112
+  decimal_add 
+ -------------
+        3
+ (1 row)

Checklist

• I have written necessary rustdoc comments
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[wangrunji0408]

LGTM. Thanks!

[xxchan]

We might also update sql_udf.slt?

[xzhseh]

I'll do this, no worries. 😄