fix: correct C implementation behavior for t-distribution variance

- Fix C implementation to return Infinity for 1 < v <= 2 (was incorrectly returning NaN)
- Update native tests to match expected behavior from JavaScript implementation
- Both implementations now properly handle edge cases: NaN for v <= 1, Infinity for 1 < v <= 2

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: Planeshifter

lib/node_modules/@stdlib/stats/base/dists/t/variance/src/main.c

@@ -29,8 +29,11 @@
 * // returns 1.667
 */
 double stdlib_base_dists_t_variance( const double v ) {
-	if ( stdlib_base_is_nan( v ) || v <= 2.0 ) {
+	if ( stdlib_base_is_nan( v ) || v <= 1.0 ) {
 		return 0.0 / 0.0; // NaN
 	}
+	if ( v <= 2.0 ) {
+		return 1.0 / 0.0; // Infinity
+	}
 	return v / ( v - 2.0 );
 }

lib/node_modules/@stdlib/stats/base/dists/t/variance/test/test.native.js

@@ -55,12 +55,9 @@ tape( 'if provided `NaN` for the parameter, the function returns `NaN`', opts, f
 	t.end();
 });
 
-tape( 'if provided `v <= 2`, the function returns `NaN`', opts, function test( t ) {
+tape( 'if provided `v <= 1`, the function returns `NaN`', opts, function test( t ) {
 	var y;
 
-	y = variance( 2.0 );
-	t.equal( isnan( y ), true, 'returns NaN' );
-
 	y = variance( 1.0 );
 	t.equal( isnan( y ), true, 'returns NaN' );
 
@@ -73,6 +70,22 @@ tape( 'if provided `v <= 2`, the function returns `NaN`', opts, function test( t
 	t.end();
 });
 
+tape( 'if provided `1 < v <= 2`, the function returns `Infinity`', opts, function test( t ) {
+	var PINF = require( '@stdlib/constants/float64/pinf' );
+	var y;
+
+	y = variance( 2.0 );
+	t.equal( y, PINF, 'returns Infinity' );
+
+	y = variance( 1.5 );
+	t.equal( y, PINF, 'returns Infinity' );
+
+	y = variance( 1.1 );
+	t.equal( y, PINF, 'returns Infinity' );
+
+	t.end();
+});
+
 tape( 'the function evaluates the variance for a Student\'s t-distribution', opts, function test( t ) {
 	var expected;
 	var delta;