[DEV-14673] Remove old network module and add moved block

[ltellesfl]

Note

Medium Risk
Touches core networking/state migration; incorrect moved addresses or SG wiring could lead to unintended resource replacement or connectivity issues during apply.

Overview
Standardizes on the networking module by removing the public_networking option and the network_module variable, and updating locals/module wiring to always source VPC/subnet/SG outputs from module.networking when creating the environment.

Simplifies downstream consumers to always use environment_all_subnets_sg_id (e.g., karpenter, lambda-sns-forwarder, efs-storage, fsx-storage, and EKS cluster_additional_security_group_ids) instead of conditionally selecting between security groups.

Adds Terraform moved blocks to migrate public_networking VPC and subnet resources into the new networking module path to avoid destroy/recreate during upgrade.

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[ashmuck]

lgtm