Implements OpenTelemetry Instrumentation for Observability

[shikokuchuo]

Closes #394.

Current behaviour:

• daemons(n) creates a persistent otel span
• mirai() fires an event with a child span
• Evaluation of the mirai() call on the daemon activates child span (for duration of evaluation)
  • Includes daemon identifier as an attribute so we know where it ran
• daemons(0) ends the persistent span

Test using:

pak::pak("r-lib/mirai@feat-otel")

library(mirai)
daemons(2)
m1 <- mirai(Sys.sleep(2))
m2 <- mirai(Sys.sleep(2))
m1[]
m2[]
daemons(0)