feat: attach Diagnostic to "invalid function argument types" error

[choplin]

Which issue does this PR close?

• Closes Attach Diagnostic to "invalid function argument types" error #14431

Rationale for this change

When a scalar or aggregate function is called with argument types that don't match any supported signature (e.g. SELECT sum('a')), the error message is a raw text dump with no source location. This PR attaches a Diagnostic so downstream consumers can highlight the offending call site in the original SQL query.

What changes are included in this PR?

• Add spans: Spans field to ScalarFunction and AggregateFunction so function-call source locations survive planning and optimization.
• Populate spans from sqlparser in the SQL planner when collect_spans is enabled, following the same pattern used for Column.
• In verify_function_arguments, attach a Diagnostic with:
  • message: the function name (invalid argument type(s) for 'sum')
  • span: the function call site in the original SQL
  • note: the actual argument types (called with argument type(s): Utf8)
  • help: the candidate signatures (candidate function(s): sum(Decimal), sum(UInt64), ...)
• Update all pattern matches, tree-node transforms, and serialization code for the new spans field.

Are there any user-facing changes?

No breaking API changes. ScalarFunction and AggregateFunction gain a spans: Spans field, but Spans is ignored in PartialEq / Hash and defaults to empty, so existing code using ScalarFunction::new_udf / AggregateFunction::new_udf is unaffected.

When an error occurs, a diagnositc is attached in the error message.

Before (no Diagnostic attached):

Error during planning: No function matches the given name and argument types 'sum(Utf8)'. You might need to add explicit type casts.
	Candidate functions:
	sum(Decimal)
	sum(UInt64)
	sum(Int64)
	sum(Float64)
	sum(Duration)

After (same error message, with Diagnostic now attached):

Error during planning: No function matches the given name and argument types 'sum(Utf8)'. You might need to add explicit type casts.
	Candidate functions:
	sum(Decimal)
	sum(UInt64)
	sum(Int64)
	sum(Float64)
	sum(Duration)

Diagnostic:
  message: invalid argument type(s) for 'sum'
  span:    1:8 - 1:11
  note:    called with argument type(s): Utf8
  help:    candidate function(s): sum(Decimal), sum(UInt64), sum(Int64), sum(Float64), sum(Duration)