fix(race): fixing race condition found with test harness

[guergabo]

Changes

• Add a buffered channel of size 1 to get rid of race condition.
• Update the callback to just write to the channel since a write to a closed channel already causes a panic.

Context
I made the assumption the sendOrPanic only cares that the api goroutine didn't die and is available to complete the request. Since we defer the close() in the api goroutine, it means that if the kernel can write to the channel (without panicing), the api layer goroutine is available and has not exited or paniced. so should be same behavior as before minus race condition.

[codecov]

Codecov Report

Merging #107 (41048d7) into main (9b14fce) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #107      +/-   ##
==========================================
- Coverage   67.18%   67.16%   -0.03%     
==========================================
  Files          57       57              
  Lines        5949     5944       -5     
==========================================
- Hits         3997     3992       -5     
  Misses       1667     1667              
  Partials      285      285              

Files	Coverage Δ
internal/app/subsystems/api/service/service.go	87.43% <100.00%> (-0.30%)	⬇️

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