Implement get_transceiver_dom_flags for SFF-8636 modules

[lotus-nexthop]

Description

Implement get_transceiver_dom_flags() on Sff8636Api, reading the latched free side monitor interrupt flags (SFF-8636 Rev 2.12 Table 6-6, lower page 00h byte 6 = temperature, byte 7 = supply voltage, bits 7–4). The returned dict uses the same key schema as the CMIS implementation.

Fixes sonic-net/sonic-buildimage#28779

Motivation and Context

show platform temperature reports Warning=N/A for every xSFP row backed by a non-CMIS (SFF-8636/QSFP28) module.
get_transceiver_dom_flags() was only ever implemented for CMIS/eLSFP; for SFF-8636 the base class raises NotImplementedError, so xcvrd silently skips writing TRANSCEIVER_DOM_FLAG for those ports. This gap was latent until two upstream changes merged 2026-05-13 moved the Warning column's source onto that table:

• sonic-net/sonic-platform-daemons#808 removed per-SFP rows from thermalctld's TEMPERATURE_INFO (perf fix). thermalctld had computed warning_status leniently — missing data defaulted to False.
• sonic-net/sonic-utilities#4522 made tempershow build xSFP rows from xcvrd's DOM tables, deriving Warning from TRANSCEIVER_DOM_FLAG and rendering N/A when absent.

How Has This Been Tested?

Validated live on hardware

Before fix

$ show platform temperature
                      Sensor    Temperature    High TH    Low TH    Crit High TH    Crit Low TH    Warning          Timestamp
----------------------------  -------------  ---------  --------  --------------  -------------  ---------  -----------------
...
         xSFP module 35 Temp          0            N/A       N/A             N/A            N/A        N/A  20260731 23:38:42
         xSFP module 36 Temp          0            N/A       N/A             N/A            N/A        N/A  20260731 23:38:42
         xSFP module 37 Temp          0            N/A       N/A             N/A            N/A        N/A  20260731 23:38:42
         xSFP module 38 Temp          0            N/A       N/A             N/A            N/A        N/A  20260731 23:38:42

After fix

$ show platform temperature
                     Sensor    Temperature    High TH    Low TH    Crit High TH    Crit Low TH    Warning          Timestamp
----------------------------  -------------  ---------  --------  --------------  -------------  ---------  -----------------
...
         xSFP module 36 Temp          0            N/A       N/A             N/A            N/A      False  20260801 00:46:25
         xSFP module 37 Temp          0            N/A       N/A             N/A            N/A      False  20260801 00:46:25
         xSFP module 38 Temp          0            N/A       N/A             N/A            N/A      False  20260801 00:46:25

Additional Information (Optional)

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines:
There may be pipelines that require an authorized user to comment /azp run to run.

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines:
Successfully started running 1 pipeline(s).

[azure-pipelines]

Azure Pipelines:
There may be pipelines that require an authorized user to comment /azp run to run.

[prgeor]

@lotus-nexthop why are these fields still showing NA? Don't we need to fix?

Temperature High TH Low TH Crit High TH Crit Low TH

[Copilot]

Pull request overview

This PR extends the sonic_platform_base transceiver abstraction by implementing get_transceiver_dom_flags() for SFF-8636 (QSFP28) modules, aligning its returned flag schema with the existing CMIS implementation so higher-level consumers can uniformly populate TRANSCEIVER_DOM_FLAG.

Changes:

• Implement Sff8636Api.get_transceiver_dom_flags() by reading and decoding the latched interrupt flag bytes for temperature and Vcc.
• Add new EEPROM field definitions (TempFlags, VccFlags) to the SFF-8636 public memory map and constants.
• Add pytest coverage for the new DOM-flag decoding behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/sonic_xcvr/test_sff8636.py	Adds unit tests validating SFF-8636 DOM flag decoding and EEPROM read behavior.
sonic_platform_base/sonic_xcvr/mem_maps/public/sff8636.py	Adds whole-byte fields for the latched temp/Vcc flag bytes to avoid per-bit clearing reads.
sonic_platform_base/sonic_xcvr/fields/consts.py	Introduces new field-name constants used by the SFF-8636 mem map and API.
sonic_platform_base/sonic_xcvr/api/public/sff8636.py	Implements DOM flag retrieval/decoding for SFF-8636 modules using the CMIS-compatible key schema.