Adds Send + Sync to Async instruments (metrics)

[markdingram]

• Allow metrics instruments to be cloned #280 added this to sync instruments previously

[codecov]

Codecov Report

Merging #422 (d8ba96c) into master (37b64b4) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
- Coverage   48.34%   48.32%   -0.02%     
==========================================
  Files          65       65              
  Lines        5502     5502              
==========================================
- Hits         2660     2659       -1     
- Misses       2842     2843       +1     

Impacted Files	Coverage Δ
...ntelemetry/src/sdk/metrics/aggregators/ddsketch.rs	76.76% <0.00%> (-0.20%)	⬇️

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[TommyCpp]

There are some places in sdk uses Arc<dyn AsyncInstrumentCore + Send + Sync> now. Could simplify it to Arc<dyn AsyncInstrumentCore>
For example,

opentelemetry-rust/opentelemetry/src/sdk/metrics/mod.rs

Lines 81 to 88 in 37b64b4

	struct AsyncInstrumentState {
	/// runners maintains the set of runners in the order they were
	/// registered.
	runners: Vec<(
	AsyncRunner,
	Arc<dyn sdk_api::AsyncInstrumentCore + Send + Sync>,
	)>,
	}

[jtescher]

@TommyCpp good catch, yeah those should get cleaned up.

[markdingram]

@TommyCpp good catch, yeah those should get cleaned up.

Happy to do this!