Use VBlank interrupt in unbricked examples

[zhangsan1890]

Fixes #157.

This updates the unbricked examples to use the VBlank interrupt for frame timing instead of polling rLY in the main loop.

Changes:

• add a VBlank interrupt handler and WaitForVBlank helper to the affected examples
• enable VBlank interrupts during initialization
• keep serial interrupt handling working in the serial-link examples by enabling both Serial and VBlank interrupts

Verification:

• git diff --check
• checked there are no remaining WaitVBlank2 / .wait_vblank_* main-loop polling patterns in unbricked examples
• bash unbricked/build_all.sh