opentelemetry-sdk: update iterator for BoundedList

[codeboten]

Description

Return the list of keys instead of a copy of the BoundedList in a deque.

Type of change

Please delete options that are not relevant.

• small perf improvement

How Has This Been Tested?

Ran the benchmark 10x and got the following output:

Type	Items	CPU Before (µs)	CPU After (µs)	CPU Δ	Mem Before (B)	Mem After (B)	Mem Δ
events	1	6.0	6.0	-1.0%	1,580	964	-39.0%
events	10	16.2	16.1	-0.4%	1,708	964	-43.6%
events	50	61.1	61.1	-0.0%	1,996	1,140	-42.9%
events	128	149.3	149.0	-0.2%	3,660	2,372	-35.2%
links	1	5.6	5.4	-2.5%	1,580	964	-39.0%
links	10	12.0	12.1	+0.5%	1,708	964	-43.6%
links	50	41.4	41.1	-0.6%	1,996	1,140	-42.9%
links	128	98.7	100.2	+1.5%	3,660	2,372	-35.2%

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Benchmark tests have been updated
• Documentation has been updated