feat: add ceil, cos, sin, sqrt, isNan native methods and division-by-zero tests

Implement five new Num methods (ceil, cos, sin, sqrt, isNan) in wren_core.c and register them on the Num class. Add corresponding test files for ceil, floor, is_nan, and sqrt. Extend divide.wren with division-by-zero edge cases (inf, -inf, nan). Remove stale TODO comments from minus, multiply, and plus tests.

test/number/floor.wren

@@ -0,0 +1,8 @@
+IO.print(123.floor)    // expect: 123
+IO.print(-123.floor)   // expect: -123
+IO.print(0.floor)      // expect: 0
+IO.print(-0.floor)     // expect: -0
+IO.print(0.123.floor)  // expect: 0
+IO.print(12.3.floor)   // expect: 12
+IO.print(-0.123.floor) // expect: -1
+IO.print(-12.3.floor)  // expect: -13