[Bug]: Off-route recalculation is very slow (up to ~30s) with NavigationTravelMode.taxi

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Package version

google_navigation_flutter 0.9.4

### Flutter / Dart version

Flutter 3.44.4 (stable), Dart SDK >=3.3.4 <4.0.0

### Platform

Android (physical devices in a live taxi fleet)

### Description

We run a taxi-driver app on top of this SDK. Navigation is started with
`GoogleMapsNavigator.setDestinations(...)` using **`travelMode: NavigationTravelMode.taxi`**,
then `startGuidance()`.

Drivers are reporting that when they leave the suggested route, for example they take a
different street to avoid traffic, or a passenger asks for another way, the SDK is very
slow to recalculate a new route. They report waiting up to roughly **30 seconds** before
guidance snaps to a new route. Until that happens the on-screen guidance keeps pointing
back at the old route, which is confusing while actively driving.

For a taxi app this is a serious problem. Drivers go off-route constantly and every
second of stale guidance is real money (wrong turns, longer trips, unhappy passengers).
We need near-instant rerouting, the way the consumer Google Maps app reroutes almost
immediately after a missed turn.

We tested this **side by side on Android**: our app (built on google_navigation_flutter)
against the consumer **Google Maps** app, on the same device under the same conditions.
Google Maps reroutes almost instantly after going off-route, while our app built on this
SDK takes far longer (up to ~30s) to recalculate.

We would really appreciate you looking into this. Specifically:

1. Is the off-route detection / reroute latency configurable in any way (a threshold,
debounce, or minimum off-route distance)? We do not see an option for it.
2. Does **`NavigationTravelMode.taxi`** get routed differently from `driving` on the
backend in a way that increases recalculation time? Would switching to `driving`
reroute faster?
3. Is there anything on our side we can call to force or speed up a recalculation when
we detect the driver is off-route?

### Our routing setup

```dart
final routeStatus = await GoogleMapsNavigator.setDestinations(
Destinations(
routingOptions: RoutingOptions(
travelMode: NavigationTravelMode.taxi,
routingStrategy: navigationRoutingStrategy, // defaultBest or shorter
avoidTolls: avoidTolls,
),
waypoints: widget.waypoints,
displayOptions: NavigationDisplayOptions(
showDestinationMarkers: true,
showStopSigns: true,
showTrafficLights: true,
),
),
);
await GoogleMapsNavigator.startGuidance();
```

### Steps to reproduce

1. Start guidance to a destination with `travelMode: NavigationTravelMode.taxi`.
2. While guidance is active, deliberately drive off the suggested route (turn onto a
different road).
3. Observe how long it takes for the SDK to abandon the old route and present a new
recalculated route.

### Expected behavior

Reroute should happen within a couple of seconds of going off-route, similar to the
consumer Google Maps app on the same Android device.

### Actual behavior

Recalculation can take up to ~30 seconds; guidance stays on the stale route in the
meantime. The consumer Google Maps app, tested side by side on the same Android device,
reroutes almost immediately.