fix: upgrade containerd and related logic to allow parsing new containerd flags

[Cicada1107]

Description

-info flag is a flag that was added in the containerd v2.x update and since urunc currently uses containerd v1.x to power the containerd-urunc-shim-v2 bianry, it cannot parse this flag as the old version does not have the logic to parse this new flag.
In a recent update containerd made changes to the paths to various dependencies and other structural changes.
This PR migrates urunc to the latest containerd version - containerd v2.x and makes the required changes to fix the breakages this migration causes in urunc, by accounting for the v2.x changes.

Related Issues

fixes #750

How was this tested?

• make reported no errors (build successful)
• make lint (lint successful for changes introduced in this PR)
• manual testing:
  • ran sudo nerdctl run -d --runtime io.containerd.urunc.v2 harbor.nbfc.io/nubificus/urunc/nginx-qemu-unikraft-initrd:latest
  • ran journalctl -eu containerd.service -n 100 | cat
  • checked and didn't find the level=error msg=failed to load runtime info... flag provided but not defined.. error.
• Also ran go run ./cmd/containerd-shim-urunc-v2 -info and found no errors

LLM Usage

Gemini 3.1 Pro

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl). (make test_docker passes completely)
• If LLMs were used: I have read the llm policy.

[netlify]

✅ Deploy Preview for urunc canceled.

Name	Link
🔨 Latest commit	a5128eb
🔍 Latest deploy log	https://app.netlify.com/projects/urunc/deploys/6a55ea178633c600085b6b35

[cmainas]

Hello @Cicada1107 ,

please read the contribution guide.

[Cicada1107]

Hi @cmainas,

I apologize for any inaccuracies, but I'm fairly new to urunc and after reviewing the contribution guide, I'm still not entirely sure which requirement my PR is currently missing - I wasn't sure if the concern is commit organization, Code Logic, CI Requirements or something else

Could you just very briefly point me to the issue or confirm if it is indeed the commit organization (should I split the changes further into multiple commits based on change logic?) so that I can address it correctly?

I'm trying to be responsible and would appreciate any guidance.
Thanks!

[cmainas]

Hello @Cicada1107 ,

please do not overwrite the PR template.

[Cicada1107]

Hey @cmainas I have revamped the PR to align with the PR Guidelines. This PR follows the first approach I mentioned on slack - migrating containerd to v2.

PTAL when you get the time. Thanks!

And a small doubt: when I ran the make lint command, all the changes I made, are passing with no issues, however, Line 91 in cmd/urunc/create.go does not conform to the linter as it is an ineffectual assignment. I however, have not made any changes to that file, and so as per the Contribution guide's suggestion to not alter things unrelated to the issue being solved, I have not made any changes to that. Let me know if I should change that anyway (It would simply involving removing line 91).

LMK if you need clarification for any change or if there are any changes I should make and I will resolve them ASAP.