test(nes): modularize conformance suite and add NESdev emulator test ROMs

src/system/nes/conformance/root.zig

@@ -0,0 +1,19 @@
+// ponytail: root module aggregating all subsystem conformance test modules
+const std = @import("std");
+
+pub const helpers = @import("helpers.zig");
+pub const cpu = @import("cpu.zig");
+pub const ppu = @import("ppu.zig");
+pub const apu = @import("apu.zig");
+pub const mapper = @import("mapper.zig");
+pub const input = @import("input.zig");
+pub const misc = @import("misc.zig");
+
+test {
+    _ = cpu;
+    _ = ppu;
+    _ = apu;
+    _ = mapper;
+    _ = input;
+    _ = misc;
+}