feat(interactions): add automatic_continuation to interactions.create in the TypeScript SDK

Foreground `interactions.create()` calls are capped per request by the server (32k output tokens unary, 64k streaming) and stop with `status='requires_continuation'` plus a `continuation_token`. `GeminiNextGenInteractions.create` now accepts `automatic_continuation` (default `true`) on `params` and chains continuation hops client-side so a plain `create()` returns the full decode.

Request chaining:
- Each hop after the first sends the `continuation_token` from the previous hop. With `store !== false` (default) it sets `previous_interaction_id` to the hop that issued the token and omits `input`; with `store: false` it resends the original `input`.
- Unary foreground model calls default `generation_config.max_output_tokens` to 65536 when unset without mutating caller objects (streaming uses the server's 64k default). Explicit values are never overridden.
- Stops on `completed`, `incomplete` (token preserved for manual resumption), `requires_action`, `failed`, `cancelled`, a missing token, or a repeated token. Skipped for `agent` / `agent_config` requests and `background: true`; `background: true` with `automatic_continuation: false` throws an error upfront.

Unary (`stream: false`) merging:
- Hops are merged into one `Interaction`: `steps` concatenated in hop order (leading `user_input` steps dropped on later hops), `usage` counts and per-modality breakdowns summed across hops with `usage.initial_input_tokens` taken from hop 1, `id` / `status` / `continuation_token` / `updated` from the final hop, and `previous_interaction_id` / `created` / `input` from hop 1.
- `continuation_ids` lists every hop id in order, de-duplicated with any server-provided ids. `output_text` skips intervening thought steps across hop boundaries.

Streaming (`stream: true`):
- Events from all hops are yielded verbatim on a pull-on-demand `Stream<InteractionSSEEvent>`. Consumers should treat `interaction.completed` with `status='requires_continuation'` as intermediate.
- Mid-hop transport drops or premature EOF resume from the latest `interaction.status_update` checkpoint token when no content was yielded since that checkpoint (up to 3 no-progress reconnects). SSE `error` events are terminal; HTTP status retries stay with `options.retries`.

Timeouts and errors:
- Numeric per-call `options.timeout_ms` (and alias `options.timeout`) bounds the whole `create()` call across hops via `CallDeadline`. Client-level `httpOptions.timeout`, `options.retries`, and `AbortSignal` apply per hop.
- A failure or timeout after progress throws `ContinuationInterruptedError` (`cause` chained) carrying `partialInteraction` (unary), `continuationToken`, `interactionId`, and `continuationIds` so billed work is preserved for manual resumption. First-hop failures propagate unchanged.

Opt-out:
- `automatic_continuation: false` returns the single server response untouched (no budget injection, no merging) and emits a one-time `console.warn` if it stops at `requires_continuation` without a caller-supplied `continuation_token`.

Tests: `test/unit/interactions_continuation_conformance_test.ts` (52 conformance cases) and `test/unit/interactions_continuation_test.ts` (whole-call timeout, wire hygiene, stream cancellation, and exports).
PiperOrigin-RevId: 995657093

Author: MarkDaoust