Improve error messages for incorrect zero argument signatures

[alamb]

Which issue does this PR close?

• Closes Make migration to Signature::nullary in 44.0.0 easier / less confusing #13763

Note this is a small improvement, before this PR:

• Require all zero argument UDFs use Signature::Nullary, improve error messages #13871

Rationale for this change

As described on #13763

In version s 43.0.0 and earlier of DataFusion, a TypeSignature::Any(0) means your udf could be called with zero arguments:

SELECT my_udf();

However in version 44.0.0 you get a very confusing error that says zero arguments are not supported but then gives you a candidate function is the one it just said was not supported:

SELECT my_udf();

Error during planning: example_union does not support zero arguments. 
No function matches the given name and argument types 'my_udf()'. 
You might need to add explicit type casts.

Candidate functions:
example_union()

What changes are included in this PR?

Improve error message to direct people to nullary

Are these changes tested?

Yes by CI

Are there any user-facing changes?

[alamb]

Unless this check is present, the error messages about TypeSignature::nullary are confusing as they are shown when the function is called with zero args, even if its signature requires something else (like exact signatures, etc)