chore: project scaffold and build wiring

Initial Zig 0.16 build script wiring the public `zbench` module, the
`zbench_build` helper module for downstream `build.zig` files, an
internal `test` step, and an `example` step that compiles and runs the
bundled benchmark suite.

build.zig.zon

@@ -0,0 +1,13 @@
+.{
+    .name = .zbench,
+    .version = "0.1.0",
+    .fingerprint = 0xbb819b3c1603b711,
+    .minimum_zig_version = "0.16.0",
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+        "examples",
+    },
+    .dependencies = .{},
+}