test(ec2): add SG probe/readback rst and refresh SG lifecycle docs

[audreyll2]

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[archit-bhatnagar]

Thanks for the work here, unfortunately this now conflicts with main in securitygroup.py and dhcpoptions.py, and most of the code changes have landed through other PRs: the SG parsing/describe-shape fixes came in via #48, and the DHCP options fixes (dopt- prefix, DhcpConfiguration.N parsing, response shape) via #49. So this needs a rebase, and after that, it should shrink a lot. What's still valuable:

• the elasticnetworkinterface.py groupSet fix — please dedupe _serialize_group_set (it's defined twice) and revert the "\n".join → "".join changes in the three serializers, they diverge from the rest of the codebase
• the lifecycle rst tests (test: add EC2 networking lifecycle and dependency rst examples #30 closed without merging, so these aren't in the tree yet)

Some cleanup with the rebase: there are five [sg-debug] print() calls left in securitygroup.py (one dumps the full XML on every DescribeSecurityGroups), a commented-out _normalize_ip_permissions block, and sg_probe.sh / sg_probe_output.txt / lifecyclePRmapping.md shouldn't live in tests/; the PR body is a better place for that context.

Also, FYI, CI now runs on PRs (CLI suite ≥79% + all 7 Terraform cases), so you'll get automatic verification when you push the rebase.