LLR: Link Layer Retry implementation

[rminnikanti]

What I did

• New llrorch.cpp in orchagent
  • mock tests added to validate reference counting and expected flow
• New llrmgrd implementation as per the HLD
  • DVS tests added to verify end to end DB flow.
• LLR Flex counter support
  • Added DVS test to verify the same

Why I did it
HLD: sonic-net/SONiC#2098

How I verified it

• DVS tests (tests/test_llr.py): 12 test cases covering INI profile generation, user profile precedence, profile reference counting, end-to-end DB flow.

• Gtest mock tests (tests/mock_tests/llrorch_ut.cpp): 4 gtest cases covering LlrOrch SAI call sequencing, profile lifecycle, and reference counting.

• Depends on: LLR: Added LLR APPL_DB table names to schema sonic-swss-common#1182

• Depends on: [vslib] Add LLR profile attribute capability and port stats sonic-sairedis#1873

Details if related

test_llr.py::TestLlr::test_capability_written_to_state_db PASSED                        [  8%]
test_llr.py::TestLlr::test_ini_profile_generation PASSED                                [ 16%]
test_llr.py::TestLlr::test_port_not_published_until_both_enabled PASSED                 [ 25%]
test_llr.py::TestLlr::test_user_profile_precedence PASSED                               [ 33%]
test_llr.py::TestLlr::test_shared_profile_refcount PASSED                               [ 41%]
test_llr.py::TestLlr::test_profile_change_while_active PASSED                           [ 50%]
test_llr.py::TestLlr::test_cable_speed_delete_on_llr_active_port PASSED                 [ 58%]
test_llr.py::TestLlr::test_llr_port_del_removes_appl_db PASSED                          [ 66%]
test_llr.py::TestLlr::test_invalid_config_db_profile_falls_back_to_ini PASSED           [ 75%]
test_llr.py::TestLlr::test_late_profile_arrival_rebinds_port PASSED                     [ 83%]
test_llr.py::TestLlr::test_cable_before_llr_port_backfill PASSED                        [ 91%]
test_llr.py::TestLlr::test_llr_config_recovery_after_invalid_cable_speed PASSED         [100%]

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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