fix(sensors): propagate equal_value_threshold to dynamic DataValidators

[ARYA-mgc]

Found this while comparing set_timeout() and set_equal_value_threshold() in DataValidatorGroup timeout stores _timeout_interval_us and applies it in add_new_validator(), but the threshold setter had no equivalent storage. Confirmed via the test file, which already had TODO comments flagging this exact gap and worked around it manually.

Added _equal_value_threshold member (mirrors _timeout_interval_us), applied it in add_new_validator(), removed the workaround + TODOs, added an assertion to lock in correct behavior.

This is my first PR to PX4 - happy to adjust based on any feedback.

[github-actions]

🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: 8 byte (0 %)]

    FILE SIZE        VM SIZE    
 --------------  -------------- 
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    +3.6%      +4  +3.6%      +4    DataValidatorGroup::DataValidatorGroup()
    +7.1%      +4  +7.1%      +4    sensors::VehicleOpticalFlow::ClearAccumulatedData()
     +17%      +2   +17%      +2    DataValidatorGroup::set_equal_value_threshold()
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px4_fmu-v6x [Total VM Diff: 24 byte (0 %)]

    FILE SIZE        VM SIZE    
 --------------  -------------- 
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     +12%      +6   +12%      +6    DataValidatorGroup::add_new_validator()
    +3.6%      +4  +3.6%      +4    DataValidatorGroup::DataValidatorGroup()
     +44%      +4   +44%      +4    g_nullstring
     +17%      +2   +17%      +2    DataValidatorGroup::set_equal_value_threshold()
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Updated: 2026-07-06T17:40:25

[ARYA-mgc]

Hi @mrpollo, sorry to tag you directly and add noise to your notifications - I wasn't sure who else to reach for this area.
This is a small, self-contained fix (sensors/testing) with a test added to lock in the behavior. All checks are passing. Would you be able to take a look when you have a moment, or point me to someone who covers this area? No rush at all - just following up
Thanks for your time!