Fix standardizeMissing indicator handling

[sahilphad07-sudo]

standardizeMissing rejected empty and matrix indicators for numeric inputs due to an unnecessary isvector validation check.

This change removes the isvector restriction for numeric indicators, allowing empty and matrix indicators to be handled correctly and matching MATLAB behavior.

Before

octave:> standardizeMissing([1 2 3], [])
error: standardizeMissing: INDICATOR must be a scalar or a vector.

octave:> standardizeMissing([1 2 3; 4 5 6], [1 9; 8 5])
error: standardizeMissing: INDICATOR must be a scalar or a vector.

After

octave:> standardizeMissing([1 2 3], [])
ans =

   1   2   3

octave:> standardizeMissing([1 2 3; 4 5 6], [1 9; 8 5])
ans =

   NaN     2     3
     4   NaN     6

MATLAB Behavior

>> standardizeMissing([1 2 3], [])
ans =

     1     2     3

>> standardizeMissing([1 2 3; 4 5 6], [1 9; 8 5])
ans =

   NaN     2     3
     4   NaN     6

Regression Tests Added

• Empty indicator
• Matrix indicator

Test Results

All existing and new standardizeMissing BISTs pass:

PASSES 65 out of 65 tests.