Use async keyboard report sending in matrix scanning

[HaoboGu]

Now the matrix scanning result is sent key processor using try_send, which might result in missing key event when typing fast. Changing to async send might slow down the scanning rate when the channel is full, but no more missing key.

[github-actions]

PR build size

  text	   data	    bss	    dec	    hex	filename
120352	    116	  41308	 161776	  277f0	rmk-nrf52840

Diff

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.8% +9.57Ki  [ = ]       0    .debug_str
  +0.5% +3.99Ki  [ = ]       0    .debug_info
  +2.1% +3.85Ki  [ = ]       0    .debug_loc
  +0.6%    +592  [ = ]       0    .debug_ranges
  +0.3%    +260  +0.3%    +260    .text
  +0.2%    +215  [ = ]       0    .debug_line
  +0.1%     +32  [ = ]       0    .symtab
  +0.1%     +12  [ = ]       0    .debug_frame
  -0.2%      -1  [ = ]       0    .defmt
 -10.9%      -7  [ = ]       0    [Unmapped]
  -0.0%      -8  [ = ]       0    .debug_aranges
  -0.1%    -112  [ = ]       0    .strtab
  +0.7% +18.4Ki  +0.2%    +260    TOTAL