Update metric benchmarks

[utpilla]

Changes

• Update metrics benchmarks for API
• Use iter_batched method to generate the dynamic attributes before each iteration

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.0%. Comparing base (ae6e2ff) to head (d80580e).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1907   +/-   ##
=====================================
  Coverage   75.0%   75.0%           
=====================================
  Files        122     122           
  Lines      20289   20289           
=====================================
+ Hits       15221   15222    +1     
+ Misses      5068    5067    -1     

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[lalitb]

Thanks for fixing these. Should we also add the benchmarks results as done here -

opentelemetry-rust/opentelemetry/benches/anyvalue.rs

Lines 6 to 10 in ad990d6

	// Results:
	// CreateOTelValueString 1-2 ns
	// CreateOTelAnyValueString 15 ns
	// CreateOTelValueInt 1-2 ns
	// CreateOTelAnyValueInt 15 ns

also add the machine configuration used for testing.

[utpilla]

This benchmark method runs much faster when run in isolation. It takes around 80 ns instead of 110 ns.