fix: implement proper SRAM mirroring and stub Flash

src/bus/GamePak.zig

@@ -1,6 +1,6 @@
 const std = @import("std");
 
-const Sram = @import("Sram.zig");
+const Backup = @import("backup.zig").Backup;
 const Allocator = std.mem.Allocator;
 const log = std.log.scoped(.GamePak);
 const Self = @This();
@@ -8,7 +8,7 @@ const Self = @This();
 title: [12]u8,
 buf: []u8,
 alloc: Allocator,
-sram: Sram,
+backup: Backup,
 
 pub fn init(alloc: Allocator, path: []const u8) !Self {
     const file = try std.fs.cwd().openFile(path, .{});
@@ -18,11 +18,13 @@ pub fn init(alloc: Allocator, path: []const u8) !Self {
     const buf = try file.readToEndAlloc(alloc, len);
     const title = parseTitle(buf);
 
+    const kind = Backup.guessKind(buf) orelse .Sram;
+
     const pak = Self{
         .buf = buf,
         .alloc = alloc,
         .title = title,
-        .sram = try Sram.init(alloc),
+        .backup = try Backup.init(alloc, kind),
     };
     pak.parseHeader();
 
@@ -55,7 +57,7 @@ fn lookupMaker(slice: *const [2]u8) ?[]const u8 {
 
 pub fn deinit(self: Self) void {
     self.alloc.free(self.buf);
-    self.sram.deinit();
+    self.backup.deinit();
 }
 
 pub fn get32(self: *const Self, idx: usize) u32 {