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/banktest/banked.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <sprinter.h>
+
+/* crt0_banked.s reads this constant to know how many banks to load. */
+const uint8_t n_banks = 2;
+
+void bank1_func(void) __banked;
+void bank2_func(void) __banked;
+void bank1_func2(uint16_t) __banked;
+
+extern uint16_t bank1var;
+extern uint16_t bank2var;
+
+extern uint8_t bank_pages[];   /* filled by crt0_banked.s */
+
+int main(void)
+{
+    bank1var = 1;
+    bank2var = 2;
+    puts("HOME: program start.");
+    printf("HOME: window 3 phys page = 0x%02X\n", _io_page_w3);
+    printf("HOME: bank_pages[1] = 0x%02X\n", bank_pages[1]);
+    printf("HOME: bank_pages[2] = 0x%02X\n", bank_pages[2]);
+
+    bank1_func();
+    bank2_func();
+    bank1_func2(25);
+    bank2_func();
+
+    puts("Press any key to exit...");
+    (void)getchar();
+    return 0;
+}