Reduce assertion telemetry contention

[Amaury Levé (Evangelink)]

Summary

• replace contended ConcurrentDictionary.AddOrUpdate calls with allocation-free steady-state lookup plus Interlocked.Increment
• preserve best-effort drain semantics with atomic dictionary swaps and volatile counter reads
• add coverage for concurrent updates/drains, telemetry opt-out behavior, reset behavior, and steady-state allocations

Performance

Standalone .NET 9 Release measurements over 5,000,000 operations (median of 7, five pre-populated assertion names):

Scenario	Current	Updated
Single thread	280.26 ms	101.72 ms
4 contending threads	371.49 ms	106.45 ms
Steady-state allocation	0 B	0 B

An eager GetOrAdd(key, new StrongBox<long>()) candidate was rejected because argument evaluation allocated 120 MB over the same 5,000,000 calls.

Validation

• TestFramework unit-test project builds across all target frameworks with 0 warnings and 0 errors
• 1,513 TestFramework unit tests pass on net8.0
• two independent concurrency/allocation reviews completed, with all findings addressed

Closes #10559

[Copilot]

Pull request overview

Optimizes assertion telemetry counters to reduce hot-path contention while preserving best-effort drain behavior.

Changes:

• Replaces dictionary value updates with boxed atomic counters.
• Adds concurrency, reset, opt-out, and allocation coverage.

Show a summary per file

File	Description
src/TestFramework/TestFramework/Internal/TelemetryCollector.cs	Implements atomic boxed counters and snapshot draining.
test/UnitTests/TestFramework.UnitTests/TelemetryCollectorTests.cs	Covers counting, concurrency, draining, opt-out, and allocations.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced