Cleanup and optimize code
Add comments, fix definitions
Fix rounding errors
Fix band 1 stability
mcuconf.h
Set I2C bus clock to SYSCLK (more fast)
Apply 400kHz bus I2C clock timings for 8MHz and 48Mhz clock
main.c
Remove and reset some variables
Add separate sweep for calibration (allow calibrate if sweep paused)
Increase main thread stack (need for run calibrate, possibly need execute some commands in sweep threads for reduce stack usage)
Rework display spi driver:
use DMA for read, write
add blitBitmap functions
Use DMA for color fill
More correct SPI bus control
Move color definitions to nanovna.h
Some code optimization for speed and size (save about 3k bytes)
Change grid Y resolution to 10
Fix convert from float to int (fix some rounding errors on plot)
Disable unused HAL serial
Change battery icon
