tests: add emitOnStart: false, interval clamp, and maxPolls: 0 covera…

[extolkom]

Use this description when creating the PR at https://github.com/extolkom/core/pull/new/fix/stream-account-tests:

Closes #276.

Adds targeted tests for three untested `streamAccount` behaviors in `src/tests/account.test.ts`:

- **emitOnStart: false + maxPolls: 1** — verifies the stream yields exactly one result after the first `sleep`, not immediately.
- **intervalMs clamp** — verifies `intervalMs: 500` is clamped to `1000ms` (requires two `advanceTimersByTimeAsync(500)` calls to resolve).
- **emitOnStart: true + maxPolls: 0** — verifies the stream yields nothing and never sleeps.

All tests use `vi.useFakeTimers()` to control time and `vi.advanceTimersByTimeAsync(...)` to trigger poll cycles deterministically.

npx vitest run src/tests/account.test.ts -t "emitOnStart"

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[k-deejah]

Good job so far, Kindly resolve conflicts.