examples: Implement example that triggers the dirOpenFile mock

examples/read_file.zig

@@ -0,0 +1,33 @@
+const std = @import("std");
+const Io = std.Io;
+
+const Simulator = @import("zigmulator");
+
+fn readFileProgram(init: std.process.Init) anyerror!void {
+    const created_file = try Io.Dir.cwd().createFile(init.io, "message.txt", .{});
+    var writer = created_file.writerStreaming(init.io, &.{});
+    try writer.interface.writeAll("hello from the simulated file system");
+    try writer.interface.flush();
+    created_file.close(init.io);
+
+    const opened_file = try Io.Dir.cwd().openFile(init.io, "message.txt", .{});
+    defer opened_file.close(init.io);
+
+    var buffer: [128]u8 = undefined;
+    const read_len = try opened_file.readPositionalAll(init.io, &buffer, 0);
+
+    var stdout = Io.File.stdout().writerStreaming(init.io, &.{});
+    try stdout.interface.print("Read: {s}\n", .{buffer[0..read_len]});
+    try stdout.interface.flush();
+}
+
+pub fn main(init: std.process.Init) !void {
+    var sim: Simulator = undefined;
+    sim.init(std.heap.page_allocator, init.io);
+    defer sim.deinit();
+
+    try sim.addExecutable("read_file", readFileProgram);
+    try sim.spawn("read_file", .{});
+
+    while (sim.scheduleOne()) {}
+}