Load Testing and split sdk crate

[sbihel]

Comprised of:

• a "relay" signer HTTP service;
• k6 scripts;
• the extraction of the Rust sdk part of sdk-wasm into its own crate; and
• some fixes to errors codes in Kepler.

---

Performed a cold-start run and the prod instance almost perfectly handled interactions for 300 orbits with 100 concurrent requests, at 25 req/s (0.12% failures).

running (02m10.9s), 000/100 VUs, 300 complete and 0 interrupted iterations
default   [======================================] 100 VUs  02m10.9s/10m0s  300/300 shared iters

     ✗ orbit creation is succesful
      ↳  99% — ✓ 297 / ✗ 3
     ✗ session delegation is succesful
      ↳  99% — ✓ 299 / ✗ 1
     ✓ is status 200

     checks.........................: 99.73% ✓ 1496      ✗ 4
     data_received..................: 3.3 MB 25 kB/s
     data_sent......................: 1.6 MB 12 kB/s
     http_req_blocked...............: avg=6.21ms   min=0s    med=1µs      max=353.06ms p(90)=17µs    p(95)=230.14µs
     http_req_connecting............: avg=817.85µs min=0s    med=0s       max=39.86ms  p(90)=0s      p(95)=195.14µs
     http_req_duration..............: avg=3.92s    min=105µs med=126.51ms max=47.8s    p(90)=15.53s  p(95)=24.88s
       { expected_response:true }...: avg=3.91s    min=105µs med=126.4ms  max=47.8s    p(90)=15.48s  p(95)=24.91s
     http_req_failed................: 0.12%  ✓ 4         ✗ 3296
     http_req_receiving.............: avg=245.16µs min=6µs   med=51µs     max=52.51ms  p(90)=226.1µs p(95)=526µs
     http_req_sending...............: avg=202.12µs min=3µs   med=57µs     max=10.63ms  p(90)=381µs   p(95)=665.19µs
     http_req_tls_handshaking.......: avg=5.32ms   min=0s    med=0s       max=312.07ms p(90)=0s      p(95)=0s
     http_req_waiting...............: avg=3.92s    min=93µs  med=126.25ms max=47.8s    p(90)=15.52s  p(95)=24.88s
     http_reqs......................: 3300   25.212858/s
     iteration_duration.............: avg=43.21s   min=4.84s med=49.09s   max=1m38s    p(90)=53.43s  p(95)=53.59s
     iterations.....................: 300    2.292078/s
     vus............................: 5      min=5       max=100
     vus_max........................: 100    min=100     max=100