SECENG-13376: Add getMulti() type to SecretsStoreSecret interface

[ang-cloudflare]

Summary

Adds a getMulti() method to the SecretsStoreSecret type definition, allowing workers to fetch multiple secrets from the same store in a single request.

Motivation

Workers that need multiple secrets currently call get() sequentially for each one. Each call traverses the full JSRPC → service binding → edge service → QuickSilver path, with P99 latency of 200–500ms per call. For workers fetching 2–3 secrets, this compounds to 1–3s+ at the tail.
The secrets store edge service already supports a batch endpoint (store_secrets_multi), and the proxy worker now exposes it as getMulti() via SECENG-13376. This PR adds the corresponding TypeScript type so users get autocomplete and type checking without @ts-expect-error.

Usage

// Before: sequential, 2-3 round trips
const apiKey = await env.MY_SECRET.get();
const dbPass = await env.DB_SECRET.get();
// After: single round trip from any binding in the same store
const secrets = await env.MY_SECRET.getMulti(["API_KEY", "DB_PASSWORD", "AUTH_TOKEN"]);
// secrets = { API_KEY: "...", DB_PASSWORD: "...", AUTH_TOKEN: "..." }
Only found secrets are included in the returned record.
Changes
- types/defines/secrets-store.d.ts: Added getMulti(secretNames: string[]): Promise<Record<string, string>>

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