test: replace constructor value tests with one table test

The previous commit added a separate 177-line test file for the
constructor fix. Parts of it pass without the fix, and
TestConstructedValuesDefaultStorage asserted that changing the caller's
slice after NewStringSlice(defaults...) shows up in Value(), which is
not something we want to promise.

Test Set on one constructor per value type in flag_test.go instead, next
to the other constructor tests. Each case panics without the fix.

Reference: eddb896 ("fix: initialize parsers in collection value constructors")
Assisted-by: claude:claude-opus-5-5
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

Author: Juneezee

constructor_values_test.go

@@ -2580,6 +2580,27 @@ func TestStringMap_Serialized_Set(t *testing.T) {
 	require.Equal(t, m0.String(), m1.String(), "pre and post serialization do not match")
 }
 
+func TestSliceAndMapConstructorsSet(t *testing.T) {
+	tests := []struct {
+		name  string
+		value Value
+		input string
+		want  any
+	}{
+		{"string slice", NewStringSlice("old"), "a,b", []string{"a", "b"}},
+		{"int slice", NewIntSlice(1), "2,3", []int{2, 3}},
+		{"uint slice", NewUintSlice(1), "2,3", []uint{2, 3}},
+		{"float slice", NewFloatSlice(1), "2.5,3.5", []float64{2.5, 3.5}},
+		{"string map", NewStringMap(map[string]string{"old": "v"}), "k=v", map[string]string{"k": "v"}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.NoError(t, tt.value.Set(tt.input))
+			require.Equal(t, tt.want, tt.value.Get())
+		})
+	}
+}
+
 var timestampFlagTests = []struct {
 	name     string
 	aliases  []string