perf(l2): map tiles decode with PNGdec

PNGdec (bitbank2, 1.1.6) decodes a tile a row at a time straight into
RGB565, without lodepng's 256 KB RGBA buffer; the trail overlay goes through
it too, blended by hand for palette-with-alpha and RGBA. It lives in its own
file (ui-lvgl/TilePng.cpp) because its zlib headers put DONE/EXTRA in the
global namespace. lodepng stays the fallback and the sim's decoder.

Same 20 tiles: decode 78 -> 50 ms, trails 42 -> 17.5 ms, a whole tile
170 -> 105 ms; the map with trails is pixel-identical.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

solo/wio-tracker-l2/platformio.ini

@@ -92,6 +92,7 @@ lib_deps =
   ${Wio_Tracker_L2.lib_deps}
   densaugeo/base64 @ ~1.4.0
   lvgl/lvgl @ 9.6.0   ; pinned: bump deliberately, re-test on hardware
+  bitbank2/PNGdec @ 1.1.6   ; map tiles: PNG straight to RGB565, a row at a time (ui-lvgl/TilePng.cpp)
   SD_MMC              ; map tiles on the microSD (framework libraries from here on)
   FS
   WiFi                ; on-device map download, live tiles, OTA
@@ -111,6 +112,7 @@ lib_deps =
   ${Wio_Tracker_L2.lib_deps}
   densaugeo/base64 @ ~1.4.0
   lvgl/lvgl @ 9.6.0
+  bitbank2/PNGdec @ 1.1.6
   SD_MMC
   FS
   WiFi