fix nth_value window function negates i64::MIN

[xiedeyantu]

Which issue does this PR close?

• Closes panic: nth_value window function negates i64::MIN #22222.

Rationale for this change

nth_value could panic at execution time when called with i64::MIN as the n argument. The implementation supports negative n for reverse indexing and negated the value internally, but negating i64::MIN overflows. This caused a runtime panic instead of returning a normal DataFusion error for invalid input.

What changes are included in this PR?

This PR adds validation for the second argument of nth_value so that i64::MIN is rejected before any negation occurs. Instead of panicking during execution, the function now returns a regular execution error.

This PR also adds regression coverage at two levels:

• a unit test for the nth_value window function implementation
• a sqllogictest case covering the SQL query shape that previously triggered the panic

Are these changes tested?

Yes.

The change is covered by:

1. a focused unit test in the window function implementation
2. a SQL logic test in window.slt

Validated with:

1. cargo test -p datafusion-functions-window nth_value --lib
2. cargo test -p datafusion-sqllogictest --test sqllogictests window

Are there any user-facing changes?

Yes. Queries that previously panicked when calling nth_value(..., -9223372036854775808) now return a proper execution error instead.