Add OpenTelemetry Package

[mtmk]

• Fixes NATS.Client.OpenTelemetry package #1171

[synadia-claude-reviewer]

Claude finished @mtmk's task in 2m 55s —— View job

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This PR adds a thin NATS.Client.OpenTelemetry package with two extension methods that wire NatsTelemetry.SourceName into OpenTelemetry's TracerProviderBuilder and MeterProviderBuilder. The tracing side is correct and functional. Two issues found:

1. AddNatsClientInstrumentation(MeterProviderBuilder) is a no-op (medium)

The library only instantiates an ActivitySource("NATS.Net") — there is no System.Diagnostics.Metrics.Meter created anywhere. Registering the Meter name with AddMeter(...) will succeed silently but never receive any instrument data. The docstring on NatsTelemetry.SourceName ("The same name is used for both the ActivitySource and the Meter") is therefore incorrect today. This needs to be resolved by either:

• Adding a static readonly Meter in Internal.Telemetry (to back the metrics promise), or
• Removing the MeterProviderBuilder overload and updating the docstring until metrics are actually emitted.

See inline comments on NatsTelemetry.cs:7 and NatsInstrumentationExtensions.cs:21.

2. Duplicate string constant that can silently diverge (low)

Internal.Telemetry.NatsActivitySource is hardcoded to "NATS.Net" independently of NatsTelemetry.SourceName. If the public constant is ever updated, the internal ActivitySource won't follow. The fix is one line:

// Internal/Telemetry.cs line 9
public const string NatsActivitySource = NatsTelemetry.SourceName;

The rest of the PR — the TracerProviderBuilder extension, the project structure, IsPackable inheritance from src/Directory.Build.props, target framework multi-targeting, and the tests — all look correct.

[github-actions]

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[scottf]

LGTM