Enable per-thread instances for histogram stress test

[martintmk]

Contributes to #1386

Changes

This PR enables the secondary mode for the metrics_histogram stress test where each thread gets it's own instance of meter provider:

Shared

Number of threads: 32
Throughput: 7,980,759 iterations/sec
Throughput: 7,766,680 iterations/sec
Throughput: 7,592,290 iterations/sec
Throughput: 7,229,872 iterations/sec

Per-thread

Number of threads: 32
Throughput: 92,490,062 iterations/sec
Throughput: 90,558,222 iterations/sec
Throughput: 91,087,973 iterations/sec
Throughput: 89,307,343 iterations/sec

To run the per-thread scenario run the following command:

cargo run --release --bin metrics_histogram -- 32 --per-thread

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.1%. Comparing base (0592075) to head (9a6f84c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2659   +/-   ##
=====================================
  Coverage   79.1%   79.1%           
=====================================
  Files        120     120           
  Lines      22556   22556           
=====================================
  Hits       17857   17857           
  Misses      4699    4699           

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[cijothomas]

will need to try one with PeriodicReader and see how it impacts resources, given its going to spawn new thread for each instance.