python: kubectl-us-net and diff-nautobot-understack should extend the parent ruff config

[cardoe]

AGENTS.md documents that "Most packages extend parent pyproject.toml configuration", and the OpenStack service packages do:

[tool.ruff]
# use our default and override anything we need specifically
extend = "../pyproject.toml"
target-version = "py312"

Two packages instead carry a copy-pasted [tool.ruff] / [tool.ruff.lint] block with no extend:

• python/kubectl-us-net/pyproject.toml
• python/diff-nautobot-understack/pyproject.toml

Their select lists are D, E, F, B, I, S, UP, ASYNC, which drops rules python/pyproject.toml enables for everything else: G, LOG, C4, PIE, PT, PLE, PLW, RUF, SIM. So these packages lint more weakly than the rest of the repo and won't pick up future parent-config changes. Dropping PT in particular means flake8-pytest-style isn't enforced.

Switch both to extend = "../pyproject.toml", keeping only genuinely package-specific overrides and per-file-ignores, and fix whatever the newly-enabled rules flag.

Noticed while reviewing #2205, where a new package copied the same non-extending block. Keeping that out of the PR since it's pre-existing and repo-wide.

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