fix: Median() integer overflow

[kumarUjjawal]

Which issue does this PR close?

• Closes bug: Median() encountered integer overflow and truncates integer results #19322

Rationale for this change

When calculating the median of an even-length array of integers, averaging the two middle values using add_wrapping causes incorrect results due to integer overflow.

For example, with Int8 values -85 and -56:

Expected: (-85 + -56) / 2 = -70
Actual: -85 + -56 = -141 wraps to 115, then 115 / 2 = 57

What changes are included in this PR?

• Fix calculate_median : Use add_checked to detect overflow, and fall back to a safe midpoint formula a/2 + b/2 + ((a%2 + b%2) / 2) when overflow occurs.

• Add tests

Are these changes tested?

• All previous tests pass
• Added new tests

Are there any user-facing changes?

[Jefffrey]

Thanks, these tests look great.

One suggestion, maybe add a test where we max out the values for the type (e.g. i8::MAX) on both operands to see how the code would handle those cases?

[petern48]

Nice! I know I wrote it in the issue title, but how about we remove the integer truncation part from the PR title, since this only fixes the overflow part?