Remember last session for each user (closes #619)

Signed-off-by: AnErrupTion <anerruption@disroot.org>

src/config/SavedUsers.zig

@@ -0,0 +1,22 @@
+const std = @import("std");
+
+const SavedUsers = @This();
+
+const User = struct {
+    username: []const u8,
+    session_index: usize,
+};
+
+user_list: std.ArrayList(User),
+last_username_index: ?usize,
+
+pub fn init() SavedUsers {
+    return .{
+        .user_list = .empty,
+        .last_username_index = null,
+    };
+}
+
+pub fn deinit(self: *SavedUsers, allocator: std.mem.Allocator) void {
+    self.user_list.deinit(allocator);
+}