tests: add hello2, simple, banktest smoke tests

hello2 — stdio vs conio output API comparison (fast/no-attr vs
slower/attributed), also exercises textcolor/textbackground.
simple — packed 2-bit style array bit-twiddling smoke test.
banktest — __banked function calls across two explicit banks in huge
memory mode.

hello2.c updated to call the renamed gettextmode/settextmode (see the
conio rename in 5e5e70d).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/simple/Makefile

@@ -0,0 +1,5 @@
+# Build hello.exe — uses lib/sprinter.lib in TINY memory mode.
+
+PROJ_ROOT := $(abspath $(CURDIR)/../..)
+EXAMPLE   := simple
+include $(PROJ_ROOT)/app.mk

tests/simple/simple.c

@@ -0,0 +1,46 @@
+/*
+ * hello — smoke test for the two output APIs:
+ *
+ *   stdio (printf/puts/putchar)  — FAST, no attribute (ambient colour)
+ *   conio (cprintf/cputs/putch)  — SLOWER, applies textcolor/textbackground
+ *
+ * Demonstrates textcolor/textbackground (Turbo-C-compatible names).
+ */
+
+#include <stdio.h>
+#include <conio.h>
+#include <gfx.h>
+#include <sprinter.h>
+#include <sprinter_exit.h>
+#include <errno.h>
+
+static uint8_t buff[] = {0xE4, 0x1B};
+
+uint8_t get_style(uint32_t idx) {
+    return (uint8_t)((buff[idx >> 2] >> ((idx & 3) << 1)) & 3u);
+}
+
+void set_style(uint32_t idx, uint8_t style) {
+    buff[idx >> 2] = buff[idx >> 2] & ~(3u << ((idx & 3) << 1)) | ((style & 3u) << ((idx & 3) << 1));
+}
+
+int main(void)
+{
+    for(int i = 0; i < 8; i++) {
+        dec8(get_style(i));
+        puts("");
+    }
+
+    for(int i = 0; i < 8; i++) {
+        set_style(i, (i + 1) & 3);
+    }
+    puts("");
+    for(int i = 0; i < 8; i++) {
+        dec8(get_style(i));
+        puts("");
+    }
+
+    cputs("Press any key to exit...");
+    (void)getchar();
+    return 0;
+}