feat: add cProtectedCall to lua 5.1 api

This function was missed. It doesn't seem horribly useful, but might as
well support it.

src/ziglua-5.1/lib.zig

@@ -356,6 +356,20 @@ pub const Lua = struct {
         c.lua_concat(lua.state, n);
     }
 
+    /// Calls the C function c_fn in protected mode. The function starts with only one element on its
+    /// stack, the userdata given to this function.
+    /// See https://www.lua.org/manual/5.1/manual.html#lua_cpcall
+    pub fn cProtectedCall(lua: *Lua, c_fn: CFn, userdata: *anyopaque) !void {
+        const ret = c.lua_cpcall(lua.state, c_fn, userdata);
+        switch (ret) {
+            StatusCode.ok => return,
+            StatusCode.err_runtime => return error.Runtime,
+            StatusCode.err_memory => return error.Memory,
+            StatusCode.err_error => return error.MsgHandler,
+            else => unreachable,
+        }
+    }
+
     /// Creates a new empty table and pushes onto the stack
     /// num_arr is a hint for how many elements the table will have as a sequence
     /// num_rec is a hint for how many other elements the table will have

src/ziglua-5.1/tests.zig

@@ -322,6 +322,25 @@ test "calling a function" {
     try expectEqual(@as(i64, 42), lua.toInteger(1));
 }
 
+test "calling a function with cProtectedCall" {
+    var lua = try Lua.init(testing.allocator);
+    defer lua.deinit();
+
+    var value: i32 = 1234;
+
+    const testFn = struct {
+        fn inner(l: *Lua) i32 {
+            const passedValue = l.toUserdata(i32, 1) catch unreachable;
+            if (passedValue.* != 1234) unreachable;
+            return 0;
+        }
+    }.inner;
+
+    // cProtectedCall doesn't return values on the stack, so the test just makes
+    // sure things work!
+    try lua.cProtectedCall(ziglua.wrap(testFn), &value);
+}
+
 test "string buffers" {
     var lua = try Lua.init(testing.allocator);
     defer lua.deinit();