allow programmatic configuration of Redis storage (beyond NICEGUI_REDIS_URL)

[AlePiccin]

NiceGUI currently enables Redis-backed storage by installing nicegui[redis] and setting the NICEGUI_REDIS_URL (and optionally REDIS_TIMEOUT) environment variables. This works, but relying solely on env vars makes it harder to:

• Configure apps dynamically at runtime (e.g., different Redis instances per tenant or per environment).

• Keep all configuration in one place (e.g., a Settings object via Pydantic/BaseSettings).

• Write hermetic tests that swap storage backends or inject a temporary Redis URL.

• Run multiple NiceGUI apps in the same process with different storage configs.

• Override or extend connection parameters (timeouts, SSL, credentials, pooling) without introducing more env vars.

Describe the solution you’d like

Expose a programmatic API to configure Redis storage before ui.run() (or app startup). For example, any of the following patterns would solve the problem:

Option A: method on app.storage

from nicegui import ui, app

app.storage.use_redis(
    url="redis://localhost:6379/0",
    timeout=60,               # optional; mirrors REDIS_TIMEOUT
    client=None,              # optional: accept an existing redis.Redis instance
    kwargs={},                # optional: extra connection/pool params
)

ui.label('Hello')
ui.run()

Option B: pass a backend object

from nicegui import ui
from nicegui.storage import RedisStorage

ui.run(storage_backend=RedisStorage(
    url="redis://localhost:6379/0",
    timeout=60,
    # ...other kwargs...
))

[rodja]

Thanks @AlePiccin. This reminds me of #4840 from @alydersen. But if it works would be much better than multiple env vars. Anyone up to try a pull request?