suppress telemetry from otel export

[davidhewitt]

This solves the problem of opentelemetry sdk's dependendencies calling into tracing in the export process. The way this is done is by moving to use the async exporters in a background tokio runtime which suppresses all telemetry.

In particular this leads to a much nicer experience on DEBUG level or lower, where previously there would be endless exports sending logs about http connections to logfire's servers (etc).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.47059% with 40 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/logfire.rs	73.27%	17 Missing and 14 partials ⚠️
src/internal/log_processor_shutdown_hack.rs	76.92%	6 Missing ⚠️
src/test_utils.rs	89.28%	0 Missing and 3 partials ⚠️

📢 Thoughts on this report? Let us know!

[friendlymatthew]

I'm going to have to take more time to digest this properly