feat: delta metrics

[fenos]

What kind of change does this PR introduce?

Feat

What is the new behavior?

• Support delta metrics
• Fix vulnerability reported in Fastify

Additional context

Add any other context or screenshots.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📝 Walkthrough

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Requests with malformed Content-Type headers containing tab characters are now rejected with a 400 error response.

• New Features

  • Added OTEL_METRICS_TEMPORALITY environment variable to configure metrics export temporality (DELTA or CUMULATIVE, defaults to CUMULATIVE).

Walkthrough

This pull request adds an early onRequest hook that checks the Content-Type header and responds with 400 if the header contains a tab character. It also introduces a new configuration field otelMetricsTemporality (values 'DELTA' | 'CUMULATIVE') read from OTEL_METRICS_TEMPORALITY (default 'CUMULATIVE') and used to set OTLP metric exporter temporality.

Sequence Diagram(s)

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