Migrate deprecated Envoy v2 gzip compression API to v3

[Copilot]

Summary

This PR migrates the last remaining usage of deprecated Envoy v2 API to the modern v3 API in the compression filter factory.

Problem

The codebase was still using a deprecated v2 import for gzip compression level constants:

import io.envoyproxy.envoy.config.filter.http.gzip.v2.Gzip.CompressionLevel.Enum.BEST_VALUE

This usage was in the fallback case when compression quality configuration is not provided:

val compressionLevel = Gzip.CompressionLevel.forNumber(
    group.compressionConfig.gzip?.quality
        ?: properties.compression.gzip.quality
) ?: Gzip.CompressionLevel.forNumber(BEST_VALUE)  // v2 API usage

Solution

Updated the code to use the v3 API equivalent:

val compressionLevel = Gzip.CompressionLevel.forNumber(
    group.compressionConfig.gzip?.quality
        ?: properties.compression.gzip.quality
) ?: Gzip.CompressionLevel.BEST_SPEED  // v3 API usage

The migration maintains identical behavior since both v2.BEST_VALUE and v3.BEST_SPEED have the same numeric value (1), representing the fastest compression level.

Changes

• Removed: Deprecated v2 import io.envoyproxy.envoy.config.filter.http.gzip.v2.Gzip.CompressionLevel.Enum.BEST_VALUE
• Updated: Fallback compression level to use Gzip.CompressionLevel.BEST_SPEED directly

Verification

• ✅ All existing tests pass
• ✅ Full project builds successfully without deprecation warnings
• ✅ Comprehensive scan confirms no other v2 API usage remains
• ✅ Backward compatibility maintained (same numeric values)

The codebase now exclusively uses modern Envoy v3 APIs with no deprecated dependencies.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.