Fix missing cstdint include causing build failure

[snigdhkarki]

src/event_viz.cpp uses uint8_t but dosent includes . Build fails on Linux Mint with the following error:

src/event_viz.cpp: In function ‘int main(int, char**)’:
src/event_viz.cpp:66:3: error: ‘uint8_t’ was not declared in this scope
   66 |   uint8_t* pixels = (uint8_t*)malloc(img_sz);
      |   ^~~~~~~
src/event_viz.cpp:12:1: note: ‘uint8_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
   11 | #include <sys/wait.h>
  +++ |+#include <cstdint>
   12 |
src/event_viz.cpp:66:12: error: ‘pixels’ was not declared in this scope
   66 |   uint8_t* pixels = (uint8_t*)malloc(img_sz);
      |            ^~~~~~
src/event_viz.cpp:66:30: error: expected primary-expression before ‘)’ token
   66 |   uint8_t* pixels = (uint8_t*)malloc(img_sz);
      |                              ^
src/event_viz.cpp:67:12: error: ‘pixel’ was not declared in this scope
   67 |   uint8_t *pixel;
      |            ^~~~~
make: *** [makefile:83: bin/event_viz] Error 1