Exclude client-side network errors from schema download fault metrics

[Zee2413]

Summary

Exclude client-side network errors from getSchemas.fault metrics in GetPublicSchemaTask and GetSamSchemaTask. These errors are caused by user environment issues (corporate proxies, firewalls, DNS) and are outside our control.

Problem

Analysis of the last 24 hours of telemetry data shows:

Task	Total Requests	Failures	Failure Rate
GetSamSchemaTask	10,569	949	9.0%
GetPublicSchemaTask	10,451	767	7.3%

~54% of these failures are client-side errors we cannot fix:

• SSL/TLS Certificate Issues (~35%) - Corporate proxies/firewalls intercepting HTTPS
• Network Connectivity (~11%) - Timeouts, connection resets, socket hang ups
• DNS Resolution Failures (~8%) - Cannot resolve hosts, proxy misconfiguration
• Proxy Authentication (~0.4%) - 407 errors

Solution

Added isClientNetworkError() utility that detects client-side network errors by matching known error patterns:

• SSL/TLS: self signed certificate, unable to get local issuer certificate, etc.
• Network: ECONNRESET, ETIMEDOUT, ENOTFOUND, socket hang up, etc.
• Proxy: status code 407, TOO_MANY_REDIRECTS, Parse Error: Expected HTTP

When these errors occur, the schema tasks now return gracefully instead of throwing, so they don't count as faults in our metrics.

Testing

• Added unit tests for isClientNetworkError() in Errors.test.ts
• Added tests for client network error handling in GetSchemaTask.test.ts

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