Create ELSFP memory map classes

[aditya-nexthop]

Cherry pick commits from nexthop-ai#2 to public fork since it wasn't possible to move the original PR to sonic-net

Description

Add memory-map support for ELSFP (External Laser Source Function Plug,
OIF-ELSFP-CMIS-01.0). Builds on the per-page CMIS refactor from #667.

• mem_maps/public/elsfp.py — ElsfpMemMap extends CmisFlatMemMap
  and composes pages 01h, 02h, 1Ah, 1Bh, 2Fh, 9Fh via add_pages(...).
  Excludes lane-datapath pages 10h–13h (not present on ELSFP modules).
• cmis/pages/page1a.py — ElsfpAdvertisementsFlagsCtrlPage (CMIS 1Ah,
  OIF-ELSFP Tables 4–10): module advertisements, lane faults/warnings,
  laser save/restore, alarm masks, per-lane fault/warning codes, lane
  controls, lane-to-fiber mapping, per-lane frequency.
• cmis/pages/page1b.py — ElsfpSetpointsMonitorsPage (CMIS 1Bh,
  Tables 11–12): per-lane bias-current / optical-power setpoints and
  monitors, voltage monitor, ICC monitor.
• fields/elsfp_consts.py — ELSFP field-name constants.
• codes/public/cmis.py — adds CONTROL_MODE, LANE_FAULT_CODE,
  LANE_WARNING_CODE, LANE_STATE code tables.
• cmis/pages/consts.py + __init__.py — ELSFP page-number constants
  and new-class re-exports.
• cmis/pages/page00_lower.py — adds EXTENDED_MODULE_INFO_FIELD
  (MODULE_FUNCTION_TYPE at byte 57) so ELSFP modules are identifiable
  via the standard module-info block.

Motivation and Context

ELSFP modules expose CMIS but substitute the lane-datapath pages
(10h–13h) for laser-source control pages (1Ah/1Bh) and add their own
fault/warning vocabulary. Without these classes, none of the
ELSFP-specific fields are addressable from sonic-platform-common.

The per-page memory-map refactor in #667 made this composable:
ElsfpMemMap reuses every shared CMIS page and only adds the two ELSFP
pages plus the small set of new codes/consts they reference.

How Has This Been Tested?

pytest suite: 1168 passed in 1.53s (no regressions vs master).
ElsfpMemMap(CmisCodes) instantiates cleanly and exposes the new
field groups via the inherited XcvrMemMap.get_field() lookup.

Additional Information (Optional)

Purely additive — no existing class is modified semantically.

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[Copilot]

Pull request overview

Adds ELSFP (OIF-ELSFP-CMIS-01.0) support to sonic-platform-common by introducing an ELSFP-specific CMIS memory map, new page implementations (1Ah/1Bh), and the accompanying field constants and code tables so ELSFP modules can be identified and their ELSFP-only fields can be accessed via the existing mem-map APIs.

Changes:

• Introduces ElsfpMemMap composed from standard CMIS pages plus new ELSFP pages 0x1A/0x1B (excluding CMIS lane-datapath pages 0x10–0x13).
• Adds ELSFP page implementations and ELSFP-specific field-name constants and code tables.
• Extends CMIS page 0x00 lower to expose MODULE_FUNCTION_TYPE in an EXTENDED_MODULE_INFO_FIELD, with a new unit test covering page composition and basic field/code availability.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/sonic_xcvr/test_elsfp.py	Adds unit tests for ElsfpMemMap page composition, field resolvability, and ELSFP-specific code tables.
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/pages/page1a.py	Adds ELSFP CMIS page 0x1A fields (advertisements, flags, controls, masks, lane state).
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/pages/page1b.py	Adds ELSFP CMIS page 0x1B fields (per-lane setpoints/monitors).
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/pages/page00_lower.py	Adds EXTENDED_MODULE_INFO_FIELD containing MODULE_FUNCTION_TYPE for ELSFP identification.
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/pages/consts.py	Defines ELSFP page number constants (0x1A, 0x1B).
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/pages/init.py	Re-exports ELSFP page constants and page classes.
sonic_platform_base/sonic_xcvr/mem_maps/public/cmis/elsfp.py	Adds ElsfpMemMap that composes the appropriate CMIS + ELSFP pages.
sonic_platform_base/sonic_xcvr/fields/elsfp_consts.py	Adds ELSFP-specific field-name constants for pages 0x1A and 0x1B.
sonic_platform_base/sonic_xcvr/fields/consts.py	Adds shared field-name constants for MODULE_FUNCTION_TYPE and EXTENDED_MODULE_INFO_FIELD.
sonic_platform_base/sonic_xcvr/codes/public/elsfp.py	Adds ElsfpCodes extending CMIS codes with ELSFP-specific code tables.
sonic_platform_base/sonic_xcvr/codes/public/cmis.py	Adds MODULE_FUNCTION_TYPE code table and extends VDM type entries.

[mssonicbld]

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