Update to latest build.zig API

zig version 0.11.0-dev.1638+7199d7c77

Author: joachimschmidt557

build.zig

@@ -2,11 +2,14 @@ const Builder = @import("std").build.Builder;
 
 pub fn build(b: *Builder) void {
     const target = b.standardTargetOptions(.{});
-    const mode = b.standardReleaseOptions();
+    const optimize = b.standardOptimizeOption(.{});
 
-    var main_tests = b.addTest("src/main.zig");
-    main_tests.setTarget(target);
-    main_tests.setBuildMode(mode);
+    var main_tests = b.addTest(.{
+        .name = "main test suite",
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
 
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&main_tests.step);