refactor(superdoc): type optional event callback registration

[caio-pizzol]

SD-2867 Cluster C only: type-only fix for the EventEmitter registration sites in SuperDoc.js where Config.on* callbacks are typed as optional but the public Config makes them so.

• Casts optional config callbacks at EventEmitter registration sites only — #initListeners (14 sites) and #addToolbar's toolbar.on('exception', ...) (1 site).
• The cast is a module-private asEventListener<T> identity helper; runtime returns the exact same value EventEmitter would have received before, so there is no defaulting or guard behavior change. If a consumer ever passes undefined explicitly, EventEmitter sees the same undefined it would have without the wrapper.
• Does not touch the runtime-default mismatches in Clusters A and B (initializer null vs typedef undefined, User typedef vs DEFAULT_USER shape) or the heterogeneous Cluster D fixes (provider widening, SearchMatch shape, DocumentMode literal, etc.). Those each have consumer-observable trade-offs and need a separate audit.

Boundary check (matters for SD-2828 / SD-2867 separation):
The asEventListener helper is declared at module scope inside SuperDoc.js, not on the class. grep -E "asEventListener|EventListener" packages/superdoc/dist/superdoc/src/core/SuperDoc.d.ts returns no matches — the helper does not appear in the emitted public declarations.

Verified:

• pnpm --filter superdoc check:jsdoc → 3 gated files clean
• pnpm --filter superdoc build:es → no FAIL-level findings
• node tests/consumer-typecheck/typecheck-matrix.mjs → 33 passed, 0 failed
• Closes 15 of the 44 TS2345/TS2322 sites in SuperDoc.js (exact cluster match).

[linear]

SD-2867 checkJs gate: enroll SuperDoc.js (Phase 2)

[superdoc-bot]

🎉 This PR is included in @superdoc-dev/mcp v0.3.0-next.34

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🎉 This PR is included in vscode-ext v2.3.0-next.78

[superdoc-bot]

🎉 This PR is included in superdoc v1.30.0-next.35

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[superdoc-bot]

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[superdoc-bot]

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[superdoc-bot]

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[superdoc-bot]

🎉 This PR is included in superdoc v1.32.0

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🎉 This PR is included in @superdoc-dev/react v1.3.0

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[superdoc-bot]

🎉 This PR is included in vscode-ext v2.4.0

[superdoc-bot]

🎉 This PR is included in superdoc-sdk v1.9.0