[Cilium v1.19] feat: slog/logr logging bridges and shared utilities

[nddq]

Summary

Part 3 of the Cilium v1.19 upgrade (#1788).

Foundational utilities needed by all subsequent PRs: slog/logr bridge in pkg/log/zap.go, structpb extensions in flow_utils.go, ITracer removal, metrics slog migration.

Files (12):

• pkg/log/zap.go, pkg/log/zap_test.go
• pkg/utils/flow_utils.go, pkg/utils/utils_linux_test.go
• pkg/metrics/metrics.go, pkg/metrics/metrics_test.go, pkg/metrics/types.go
• pkg/config/config.go
• pkg/common/endpoint.go
• pkg/plugin/common/common_linux.go
• pkg/plugin/common/mocks/mock_types.go (DELETE)
• pkg/hubble/common/decoder_linux.go

Estimated size: ~500 lines

Depends on: #2033
Parent issue: #1788