[Nexthop][m4062nhp] Select platform mapping and SDK YAML by switch-card revision

[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

The m4062nhp P2 switch card rewires the front panel, so a single image has to
pick the right platform mapping and HSDK YAML for the switch-card revision it
boots on.

• The platform descriptor gains an optional pmUnitVersions matcher
  (productionState, productionSubState, respinVariantIndicator), the same
  model platform_manager already uses for versionedPmUnitConfigs. The
  descriptor registry reads the chassis EEPROM once. A versioned descriptor
  that matches wins, otherwise the unversioned descriptor is the default. If
  the EEPROM cannot be read the registry warns once and uses the default.
  Platforms without a matcher are unaffected.
• SaiBcmPlatform::getHwConfig() loads the asic_config.yaml that sits next
  to the selected descriptor before falling back to the embedded config, so
  the SDK YAML follows the same revision selection as the mapping.
• m4062nhp data: platform_mapping/ is the P2 default and
  variants/m4062nhp_p1/ matches productionState=1. The variant carries its
  own descriptor, static mapping, SI settings and profile settings; the port
  profile mapping and vendor config are inherited from the base. asic_config
  grows default and p1 variants. The generator itself is unchanged apart
  from parsing the new descriptor column.
• platform_manager: the P2 SMB layout is the default with a versioned P1
  entry.

Test Plan

• Two P1 systems select m4062nhp_p1, one P2 system selects the default. The
  mapping and SDK YAML deployed on all three are byte-identical to the
  artifacts in this PR.
• P1 system A: 128/128 ports up, LLDP neighbours match the cabling database
  64/64.
• P1 system B: 17/17 present transceivers up. Turning off the laser on one cage
  drops exactly that port and its cabled peer.
• Link test passes with 5 snake pairs.
• verify_generated_files.py passes; every other platform regenerates
  byte-identical.
• pre-commit run passes.