Experimental: grpc_kit support

[palkan]

Summary

Make it possible to use grpc_kit as a gRPC server implementation.

Add grpc_kit to your Gemfile and specify ANYCABLE_GRPC_IMPL=grpc_kit env var to use it.

Checklist

• I've added tests for this change
• I've added a Changelog entry
• I've updated documentation

Benchmarks

Running k6 run echo.js --duration=10s --vus=30:

• gRPC

running (10.1s), 00/30 VUs, 300 complete and 0 interrupted iterations
default ✓ [======================================] 30 VUs  10s

     ✓ status is OK

     checks...............: 100.00% ✓ 300       ✗ 0   
     data_received........: 101 kB  10 kB/s
     data_sent............: 97 kB   9.6 kB/s
     grpc_req_duration....: avg=6.74ms min=1.18ms med=6.49ms max=18.95ms p(90)=10.88ms p(95)=12.11ms
     iteration_duration...: avg=1s     min=1s     med=1s     max=1.02s   p(90)=1.01s   p(95)=1.01s  
     iterations...........: 300     29.695843/s
     vus..................: 30      min=30      max=30
     vus_max..............: 30      min=30      max=30

• grpc_kit

running (10.1s), 00/30 VUs, 300 complete and 0 interrupted iterations
default ✓ [======================================] 30 VUs  10s

     ✓ status is OK

     checks...............: 100.00% ✓ 300       ✗ 0   
     data_received........: 58 kB   5.7 kB/s
     data_sent............: 92 kB   9.1 kB/s
     grpc_req_duration....: avg=967.66µs min=446.91µs med=864.79µs max=5.82ms p(90)=1.37ms p(95)=1.58ms
     iteration_duration...: avg=1s       min=1s       med=1s       max=1.02s  p(90)=1.01s  p(95)=1.01s 
     iterations...........: 300     29.687503/s
     vus..................: 30      min=30      max=30
     vus_max..............: 30      min=30      max=30

grpc_kit performs much better for simple requests (p85: 1.5ms < 12ms).