docs: add TSDoc for example_util, event_actions, run_config, and structured_events

[nuthalapativarun]

Problem / Solution

Four source files had missing or incomplete TSDoc on their exported functions and enum values. This PR adds @param, @returns, and @throws documentation aligned with the style used in the rest of the codebase and with adk-python.

Files changed

File	What was added
core/src/examples/example_util.ts	@param/@returns for convertExamplesToText; full @param/@returns/@throws for buildExampleSi; documents the gemini-2 model detection behavior
core/src/events/event_actions.ts	Expanded @param/@returns for createEventActions; full merge-semantics docs for mergeEventActions (dict merge vs. last-writer-wins for scalars)
core/src/agents/run_config.ts	@param/@returns/@throws for createRunConfig; documents all defaults and the maxLlmCalls > MAX_SAFE_INTEGER throw
core/src/events/structured_events.ts	Per-value JSDoc for all EventType enum members explaining what triggers each type

No source logic was changed — this is documentation-only.

Testing Plan

• Unit tests: existing suite passes (npm test — 1516 tests, 125 files)
• No manual E2E steps required for documentation-only changes
• npm run lint — no new errors
• npm run format — no formatting changes needed

Checklist

• TSDoc follows the @param name - description style used in runner.ts, base_agent.ts, and other documented files
• Enum member docs match the level of detail in adk-python equivalents
• No source logic modified
• Lint and format pass