feat: add trigonometric methods and Num.pi constant to core library

Add acos, asin, atan, atan2, tan methods to Num class and expose Num.pi constant with value π. Include corresponding C primitives in wren_core.c and test files for each new method.

doc/site/core/num.markdown

@@ -8,6 +8,23 @@ The absolute value of the number.
     :::dart
     -123.abs // 123
 
+### **acos**
+
+The arc cosine of the number.
+
+### **asin**
+
+The arc sine of the number.
+
+### **atan**
+
+The arc tangent of the number.
+
+### **atan**(x)
+
+The arc tangent of the number when divided by `x`, using the signs of the two
+numbers to determine the quadrant of the result.
+
 ### **ceil**
 
 Rounds the number up to the nearest integer.
@@ -42,6 +59,10 @@ The sine of the number.
 
 The square root of the number. Returns `nan` if the number is negative.
 
+### **tan**
+
+The tangent of the number.
+
 ### **-** operator
 
 Negates the number.
@@ -118,3 +139,6 @@ Attempts to parse `value` as a decimal literal and return it as an instance of
 
 It is a runtime error if `value` is not a string.
 
+### Num.**pi**
+
+The value of π.