sdk-trace: add SimpleSpanProcessor

[iRevive]

Reference	Link
Spec	https://opentelemetry.io/docs/specs/otel/trace/sdk/#simple-processor
Java implementation	SimpleSpanProcessor.java

I also moved SpanProcessor to the org.typelevel.otel4s.sdk.trace.processor package.

[armanbilge]

You never need non-fatal checks within the effect, if a non-fatal error has been countered the JVM has already terminated 😁

Also onError just-side-channels, so the error continues being raised. Wouldn't this possibly lead to duplicate error reporting?

[iRevive]

Good point. Let's not propagate errors, at least for now. We can reconsider the choice once we have the fully working SDK in place.

[armanbilge]

One unfortunate thing about logging in two steps it that it may be come separated if there are other interleaving logs. It might be better to make a new exception that is caused by e and log that, or assemble the string + stacktrace first and then log it atomically.

[iRevive]

By the way, does it make sense to introduce a separate interface for logging? For example:

trait Log[F[_]] {
  def info(message: => String): F[Unit]
  def error(message: => String): F[Unit]
  def error(message: => String, error: => Throwable): F[Unit]
}

We will use the cats.effect.std.Console by default. But a user can plug in any other logging backend: log4cats, odin, scribe, etc.

[armanbilge]

It all starts to feel rather circular 😅

[iRevive]

I tend to agree. Console should be more than enough for our use cases (at least now 😏 ).