[marif-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

Implements asic_config_v3 design.

In this PR, add support for more than one management port.

• mgmt_port_defaults in the ASIC data and mgmt_port_overrides in the platform config become lists with one entry per management port.
• An override merges onto the defaults entry at the same index; entries beyond the defaults list declare additional ports and must be complete.
• The generator rejects incomplete additional entries and duplicate logical or physical port identifiers.
• The Tomahawk5 and Tomahawk6 defaults and the five platform configs that override the management port are converted to the list form.

Also removed the unused core_offset_apply_all key from the platform schema together with the special_core_offset_apply_all mention in the schema field reference, since no generator reads either, and made the generator honor the already documented num_lanes_per_port platform setting.

Test Plan

Ran fboss/lib/asic_config_v3/run-helper.sh to generate asic_config_v3 output:

[3/3] Running utility command for fboss-asic-config-v3-gen.GEN_PY_EXE
Completed build for fboss-asic-config-v3-gen.GEN_PY_EXE
...
Generating ASIC config for icecube800banw/default...
Generating ASIC config for icecube800bc/default...
Generating ASIC config for icetea800bc/default...
Generating ASIC config for ladakh800bcls/rack...
Generating ASIC config for ladakh800bcls/test_fixture...
Generating ASIC config for meru800bia/default...
Generating ASIC config for montblanc/default...
Generating ASIC config for montblanc/hw_test...
Generating ASIC config for tahan800bc/chassis...
Generating ASIC config for tahan800bc/test_fixture...
Generating ASIC config for tahansb800bc/default...
Generating ASIC config for tahansb800bc/test_fixture...
Generating ASIC config for wedge800bact/default...
Generating ASIC config for wedge800bact/hw_test...
...
Configs have been written to specified output directory

The generated output is identical to the checked-in files for every platform

% git status --porcelain fboss/configs/platforms
<no changes>

Validated the ASIC and platform configs against the schemas

% python3 -m fboss.lib.asic_config_v3.test.validate_asic_configs_schemas --fboss-root fboss
...
15 passed, 0 failed