Move common type aliases, peripheral bundles, and init helpers for
ESP32-S3 boards into src/board/esp32s3.rs. Heltec V3 (146->48 lines)
and V4 (155->57 lines) become thin wrappers containing only
board-specific code (Vext GPIO pin, display reset sequence).
Update build.rs to exclude esp32s3.rs from board discovery and
mod.rs.j2 to include the shared module under an ESP feature gate.
swaits
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