[nrf fromtree] Make TestEventTrigger delegate testable and extensible

[ArekBalysNordic]

… (#31724)

• Make TestEventTrigger delegate testable and extensible

• Make TestEventTriggerDelegate base class manage multiple sub-handlers.
• Add unit tests for TestEventTriggerDelegate
• Introduce an interface for generic TestEventTrigger handlers
• Add Clear() method to Intrusive list to remove everything.
• Document the fact that emberAfHandleEventTrigger should NOT be used
• Update all examples as needed.
  • Renumber OTA and SmokeCO testevent trigger prefix to match new Matter 1.3 standard (first 16 bits == cluster ID being tested).
  • Clean-up dead code
  • Register OTA test event handler as intended.
• Add TODOs for platforms to clean-up TestEventTriggerDelegate registration.
• Updated BOOLCFG tests to use --hex-arg for PIXIT since --int-arg is too confusing with complex keys.

Issue #31723

Testing done:

• EEVSE Python tests using event triggers pass
• SMOKECO YAML tests using event triggers pass
• BOOLCFG Python tests using event triggers pass
• TC_TestEventTrigger passes
• New unit tests pass

• Fix merge issue

• Restyled by clang-format

• Fix uninitialized variable access

• Fix Ameba/Silabs build

• Fix CopyString bound

• More fixes of Ameba/Silabs build

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Co-authored-by: Restyled.io commits@restyled.io

cherry-picked from: 4cd1825