cleanup(supervisor-*): Improve code structure of supervisor crates

[rrhubenov]

Problem Statement

Preface

After #1650 is merged, the sandbox creation crates are split into 3 new ones:

• openshell-sandbox (will become openshell-supervisor)
• openshell-supervisor-process
• openshell-supervisor-network

The PR that introduced the split was intentionally naive - there were no designs applied to the code, and no new abstractions were introduced that would help with the flow and readability of the code.
The split was introduced using this rough reasoning:

1. Define what the pure network functionality is (mostly everything that the HTTP CONNECTO proxy implements)
2. Define what the pure process functionality is (mostly all isolation techniques and runtime auditing like the bypass monitor)
3. Define common requirements of both crates (types & functions)

This approach lead to a natural restructuring of the code, specifically:

• Shared types and most* functions moved to openshell-core when appropriate
• Non-shared types and modules moved to their respective crate owner (e.g. l7 module moved to network crate)
• Shared "helper" tasks/threads spawned in the openshell-supervisor a.k.a orchestrator crate (e.g. denial aggregator & activity aggregator threads)

Proposed Design

Cleanup tasks

Since the movement of the code had been done in a naive manner, a bunch of cleanup and introduction of helper abstractions can be applied. List of improvements in no particular order:

• Rename openshell-sandbox -> openshell-supervisor NOTE: Breaking
• Cleanup the pid and probe_path loops that wait for the 2 values to be available.
• Deduplicate code of procfs functions in both supervisor-network and supervisor-process (e.g. introduce new crate)
• Introduce a better entrypoint for both supervisor-network and supervisor-process (currently run_networking and run_process)
• Potentially wrap the NetworkNamespace variable in run_sandbox with a shared pointer and pass to process and network rather than having the run_sandbox hold it.
• TBD

Checklist

• I've reviewed existing issues and the architecture docs
• This is a design proposal, not a "please build this" request