Support Delta & Cumulative temporality for LastValue aggregates

[MrAlias]

The specification was updated here to have different drop behavior for delta vs cumulative temorality for both synchronous and asynchronous instruments. Specifically:

The MetricReader selection of temporality as a function of instrument kind influences the persistence of metric data points across collections. For synchronous instruments with Cumulative aggregation temporality, MetricReader.Collect MUST receive data points exposed in previous collections regardless of whether new measurements have been recorded. For synchronous instruments with Delta aggregation temporality, MetricReader.Collect MUST only receive data points with measurements recorded since the previous collection. For asynchronous instruments with Delta or Cumulative aggregation temporality, MetricReader.Collect MUST only receive data points with measurements recorded since the previous collection. These rules apply to all metrics, not just those whose point kinds includes an aggregation temporality field.

Our current implementation of the last-value aggregate does not support this change. We are not able to support a synchronous gauge (#5304) until we support this.

This introduces a new precomputedLastValue aggregation as well as both a delta and cumulative method to the lastValue aggregator to comply with the specification and unblock #5304

Note, this implements in a way to address correct start times for the last-value aggregate. However, testing for this is left to #5323.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.6%. Comparing base (737f885) to head (f1f7a41).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5305   +/-   ##
=====================================
  Coverage   84.5%   84.6%           
=====================================
  Files        268     268           
  Lines      17652   17695   +43     
=====================================
+ Hits       14930   14973   +43     
  Misses      2410    2410           
  Partials     312     312           

Files	Coverage Δ
sdk/metric/internal/aggregate/aggregate.go	100.0% <100.0%> (ø)
sdk/metric/internal/aggregate/lastvalue.go	100.0% <100.0%> (ø)
sdk/metric/pipeline.go	88.5% <100.0%> (+<0.1%)	⬆️

[dashpole]

Looks great! You got that done quick