Refactor tests into a separate module.

test/index.zig

@@ -0,0 +1,13 @@
+comptime {
+    _ = .{
+        @import("./primitive/blockcipher/aes.zig"),
+        @import("./primitive/blockcipher/operation_modes.zig"),
+        @import("./primitive/digest/sha.zig"),
+        @import("./primitive/streamcipher/chacha20.zig"),
+        @import("./primitive/streamcipher/salsa20.zig"),
+    };
+}
+
+test {
+    @import("std").testing.refAllDecls(@This());
+}