fix(metrics): detect key collisions between dimensions, metrics, and metadata

[Zelys-DFKH]

Summary

Changes

Closes #5208. In serializeMetrics(), EMF output is assembled by spreading default dimensions, dimensions, dimension sets, metric values, and metadata in that order. When keys match across those layers, later values win silently. Two of those collisions break the EMF schema:

• A metric name matching a dimension key replaces the string value with a number, so CloudWatch drops the dimension.
• A metadata key matching a metric name replaces the number with a string, so CloudWatch fails to parse the metric.

What changed

• Metrics.ts: Added a guard in storeMetric() that throws when the metric name matches any current dimension key (flat dimensions, default dimensions, or dimension sets), and a guard in addMetadata() that throws when the metadata key matches any current metric name. Both error messages include the key name.
• dimensions.test.ts: Four new tests covering a regular dimension conflict, a default dimension conflict, a dimension-set conflict (via addDimensions), and the built-in service dimension.
• metadata.test.ts: One new test covering a metadata-metric name conflict.

Issue number: Closes #5208

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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