[PUYA] Lower PUYA flash buffer to 1 page (256 B)

As discussed here: esp8266#5493 (comment)

Author: TD-er

cores/esp8266/Esp.h

@@ -25,10 +25,9 @@
 
 #define PUYASUPPORT
 #ifndef PUYA_BUFFER_SIZE
-  // Good alternative for buffer size is: SPI_FLASH_SEC_SIZE
-  // 512 bytes is a reasonable trade-off between memory use and write cycles.
+  // Good alternative for buffer size is: SPI_FLASH_SEC_SIZE (= 4k)
   // Always use a multiple of flash page size (256 bytes)
-  #define PUYA_BUFFER_SIZE 512
+  #define PUYA_BUFFER_SIZE 256
 #endif
 
 /**