Add restore network telemetry

[sjmiller609]

Summary

• add restore_network child spans around allocation, snapshot network patching, and recreate paths
• add network spans for allocation and TAP setup substeps on top of the optimized restore-network path
• preserve behavior; this PR is telemetry-only and now stacks on the host restore network optimization branch

Tests

• go test ./lib/network -count=1
• go test ./lib/network ./lib/instances -run TestRequiresRestoreConfigDiskRefresh -count=1 (lib/network passed; lib/instances fails in this checkout because embedded hypervisor and guest-agent binaries are missing)