Add `timeout=`/`wait_until=` to `Go Back` and `Go Forward`, and `referer=` to `Go To`

@Snooz82 is already working on this.

Since Aug 6, 2026.

## Use case

Two small consistency gaps in the navigation keywords:

1. **`Go Back` / `Go Forward` take no arguments at all.** `Go To` and `Reload` let users control how long to wait and which load state counts as "done" (`load`, `domcontentloaded`, `networkidle`, `commit`), but history navigation always uses the defaults. On slow pages this makes back/forward navigation flaky with no remedy — users resort to adding `Wait For Load State` or sleeps after every `Go Back`.

2. **`Go To` cannot set a referer.** Testing referrer-dependent server behavior (analytics attribution, hotlink protection, referer-based redirects) currently requires setting a context-wide `Referer` header via `New Context httpHeaders=`, which then wrongly applies to *every* request in the context instead of the one navigation.

## Proposed keyword / arguments

New named-only arguments on the existing keywords:

```
Go Back *, timeout=None wait_until=load
Go Forward *, timeout=None wait_until=load
Go To url timeout=None wait_until=load *, referer=None
```

- `timeout` — maximum navigation time (Robot Framework time format); defaults to the library timeout, same as `Go To`.
- `wait_until` — same `PageLoadStates` enum and default as `Go To`/`Reload`.
- `referer` — value of the `Referer` header for this one navigation; takes precedence over a context-wide header for this request only.

```robotframework
Go To ${DEEP_LINK} wait_until=networkidle
Go Back timeout=30s wait_until=domcontentloaded
Get Url == ${START_URL}
Go Forward wait_until=networkidle

Go To ${LANDING_PAGE} referer=https://partner.example.com/campaign
Get Text id=attribution == partner.example.com
```

## Playwright API

- [page.goBack](https://playwright.dev/docs/api/class-page#page-go-back) / [page.goForward](https://playwright.dev/docs/api/class-page#page-go-forward) (options `timeout`, `waitUntil`)
- [page.goto `referer` option](https://playwright.dev/docs/api/class-page#page-goto-option-referer)

## Implementation notes

- `protobuf/playwright.proto`: `GoBack`/`GoForward` currently take `Request.Empty` — switch to an options message carrying timeout and waitUntil; add a `referer` field to the `UrlOptions` used by `GoTo`.
- `node/playwright-wrapper`: pass the options through to `page.goBack()`/`page.goForward()`/`page.goto()`.
- Python: extend `go_back`, `go_forward`, `go_to` in `Browser/keywords/browser_control.py`; docs; stub regen; atest using the test app's redirect/slow pages, plus a referer-echo assertion.

## Backwards compatibility

Additive named-only arguments. Defaults (`timeout=None` → library timeout, `wait_until=load`, `referer=None` → no header) reproduce today's behavior exactly.