refactor(api): standardize request header key prefixes

[Ahoo-Wang]

• Introduce COSEC_EXTEND_KEY_PREFIX constant for consistent header naming
• Update AppIdCapable to use prefixed header key format
• Update DeviceIdCapable to use prefixed header key format
• Update RequestIdCapable to use prefixed header key format
• Update SpaceIdCapable to use prefixed header key format
• Create new ExtendKey.kt file with prefix constant definition

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.15%. Comparing base (8e4af7e) to head (89a8396).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #714   +/-   ##
=========================================
  Coverage     92.15%   92.15%           
  Complexity      612      612           
=========================================
  Files           149      149           
  Lines          1823     1823           
  Branches        156      156           
=========================================
  Hits           1680     1680           
  Misses           74       74           
  Partials         69       69           

Flag	Coverage Δ
unittests	92.15% <ø> (ø)

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