some effect optimizations

* getpixelcolor: attribute pure - it reads memory, but does not write
* some optimizations for SEGMENT.blur() and SEGMENT.fadeToBlackBy()

* FX.c:pp remove double calls to blur() and fade_out()
* FX.cpp: SEGMENT.setUpLeds() added to effects, to enable LED buffering (safe some time because getPixelColor does not need to access NeopixelBus)

* a few other optimizations to safe time and avoid "expensive" operations
* set I2C bus speed to 400kHz (default is 100Khz)

* a few other small optimizations and tweaks
* pio: esp32 V4 builds use "patch5" toolchain version, which contains a few bugfixes especially for memory management.

platformio.ini

@@ -915,7 +915,9 @@ lib_deps = ${esp32_4MB_M_base.lib_deps} ${common_mm.lib_deps_XL}
 board = esp32dev
 upload_speed = 460800 ; or 921600
 platform = ${esp32.platformV4}
-platform_packages = ${esp32.platformV4_packages}
+platform_packages = 
+  ${esp32.platformV4_packages}
+  toolchain-xtensa-esp32 @ 8.4.0+2021r2-patch5 ; align main tools with riscV tools
 build_unflags = ${common.build_unflags}
 build_flags = ${common.build_flags} ${esp32.build_flagsV4} ${common_mm.build_flags_S}
   -Wno-misleading-indentation -Wno-format-truncation