add SEPROXYHAL_TAG_INVALID define

[mruiz-ledger]

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.82%. Comparing base (f02cb9a) to head (3febf72).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1456   +/-   ##
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  Coverage   91.82%   91.82%           
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  Files          37       37           
  Lines        4244     4244           
  Branches      521      521           
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  Hits         3897     3897           
  Misses        257      257           
  Partials       90       90           

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unittests	91.82% <ø> (ø)

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[Copilot]

Pull request overview

Adds a dedicated constant for an “invalid”/unset SEProxyHal tag value to the protocol header, aligning with the existing tag macro pattern and reserving 0x00 as an explicit sentinel.

Changes:

• Introduce SEPROXYHAL_TAG_INVALID defined as 0x00 in include/seproxyhal_protocol.h.

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