[Bug]: JSON `createdAt` encoding differs between list and inspect output

[realrajaryan]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

Create a volume and compare createdAt in list and inspect JSON:

$ container volume create issue-vol-small -s 2MiB
issue-vol-small

$ container volume list --format json
[{"createdAt":800212872.195543,"options":{"size":"2MiB"},"sizeInBytes":2097152,"format":"ext4","source":"\/Users\/ras\/Downloads\/test_container\/audit_artifacts\/container-issue-repros-20260511-101939\/app-root\/volumes\/issue-vol-small\/volume.img","driver":"local","labels":{},"name":"issue-vol-small"}]

$ container volume inspect issue-vol-small
[
  {
    "createdAt" : "2026-05-11T17:21:12Z",
    "driver" : "local",
    "format" : "ext4",
    "labels" : {

    },
    "name" : "issue-vol-small",
    "options" : {
      "size" : "2MiB"
    },
    "sizeInBytes" : 2097152,
    "source" : "\/Users\/ras\/Downloads\/test_container\/audit_artifacts\/container-issue-repros-20260511-101939\/app-root\/volumes\/issue-vol-small\/volume.img"
  }
]

Problem description

The same JSON field uses different encodings for the same resource type. List output emits a numeric timestamp, while inspect output emits an ISO-8601 string. JSON consumers should not need different timestamp parsers for the same field.

Environment

- OS: macOS 26.4.1 (25E253)
- Xcode: Xcode 26.4.1 (17E202)
- Container: container CLI 0.12.3 (build: release, commit: f989901)

Code of Conduct

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