Span Compression: Implement Span Buffering Behavior

[astorm]

This PR represents the work needed to implement the span buffering behavior of the Compressing spans work. We will need to

• Implement the configuration gated span end buffering behavior described in the spec
• Implement the tryToCompress method fully
• Implement a preliminary isCompressionEligible method that, contrary to spec, uses the outcome AND a hard coded list of span types to determine if it's compressible

At the end of this work we will have an agent that compresses spans but is not 100% spec compliant.