[Nexthop][m4062nhp] Register m4062nhp in platform mapping verification test

[zackary-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

Registers m4062nhp in verify_generated_files.py's platform list so platform mapping generation for it is verified in OSS CI. Also applies the pre-commit ruff-check and ruff-format fixes to the same file: builtin generics in place of typing.Dict/List, a ClassVar annotation on the supported-platforms dict, INPUT_DIR imported without the alias, and formatter line reflow. No behavior change beyond the added platform.

Split out of #1394 per review feedback. Depends on #1419 , which adds the m4062nhp CSVs this test generates from, and should land first.

Test Plan

• Platform Mapping Generation Verification CI regenerates m4062nhp_platform_mapping.json from the CSVs and confirms it matches the checked-in file.
• pre-commit run --files fboss/lib/platform_mapping_v2/test/verify_generated_files.py passes clean.

[zackary-nexthop]

Closing this PR because the verification test change needs to be on the same PR as the CSVs (#1419) for the CI to pass.