fix: limit max generations

[amokan]

Naive approach to ensuring we prune ETS if there are repeated failures.

[Ziinc]

Some additional context for the other two commits:

• export_callback allows full replacement of export functionality for customization/interception of OTLP export.
• request batching functionality for reducing 413 resopnses for Request Entity Too Large #16
  • of note, i'm currently reworking the max concurrency of tasks to use the otlp max concurrent request config.
  • i'm also of the opinion that the default :otlp_concurrent_requests config of 10 is way too low, finch defaults it to 50 for http1.

@amokan will be committing to this branch to reduce conflicts.

[Ziinc]

latest round of optimizations:

• max batch size of 500
• reduced max generations to 5
• tasks are fired without limits with 6s timeouts
• max default concurrent requests is set to 50.
• reduced number of list traversals done when processing tasks