Update flake, refactor go code, add build flags

[mbssrc]

Description

Updates

• update flake and go modules
• move all go code into 'modules' folder
• renaming admin-rs to admin

Fixes

• fix various go-sec warnings
• remove unused flake input
• change sysvm trigger target from network-online to network

Changes

• introduce go build flags for hardening
• removed netvm test as functionality is replaced by dbus

Checklist

• Summary of the proposed changes in the PR description
• More detailed description in the commit message(s)
• Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• Contribution guidelines followed
• Test procedure added to nixos/tests
• Author has run nix flake check --accept-flake-config and it passes
• All automatic Github Action checks pass - see actions
• Author has added reviewers and removed PR draft status

Testing