vt: fix test failures in render and key_encode

The colors_get function used structSizedFieldFits to guard the
palette copy, which required the entire palette array to fit in the
provided size. This prevented partial palette writes when the caller
passed a truncated sized struct, since the guard failed even though
the inner code already handled partial copies correctly. Remove the
outer guard so the existing partial-copy logic applies.

The setopt_from_terminal test expected alt_esc_prefix to be false on
a fresh terminal, but the mode definition in modes.zig sets its
default to true. Update the test expectation to match.

src/terminal/c/key_encode.zig

@@ -259,7 +259,7 @@ test "setopt_from_terminal" {
 
     // Options should reflect defaults from a fresh terminal
     try testing.expect(!e.?.opts.cursor_key_application);
-    try testing.expect(!e.?.opts.alt_esc_prefix);
+    try testing.expect(e.?.opts.alt_esc_prefix);
     try testing.expectEqual(KittyFlags.disabled, e.?.opts.kitty_flags);
     try testing.expectEqual(OptionAsAlt.false, e.?.opts.macos_option_as_alt);
 }

src/terminal/c/render.zig

@@ -337,11 +337,7 @@ pub fn colors_get(
         out_colors.cursor_has_value = colors.cursor != null;
     }
 
-    if (lib.structSizedFieldFits(
-        Colors,
-        out_size,
-        "palette",
-    )) {
+    {
         const palette_offset = @offsetOf(Colors, "palette");
         if (out_size > palette_offset) {
             const available = out_size - palette_offset;