fix: support one-off charging profile timers

[ethanhawkes-gif]

Fixes #631.

ONE_OFF charging timers contain oneOffDay and omit recurringOn, but ChargingTimers.recurring_on was required. That made the reporter's charging-profile response fail during deserialization.

This change adds the oneOffDay mapping, makes the two day selectors optional, omits the unused selector on serialization, and preserves the API's HH:MM time format for both recurring and one-off timers.

Validation:

• 2 focused charging-profile tests passed
• 535 tests passed
• Ruff and Ruff format passed on the changed files
• Pyright passed
• uv lock --check passed

One theoretical edge remains: a malformed timer with neither day selector can deserialize, but its by-alias time serialization falls back to HH:MM:SS. I did not find this shape in the issue payload or open work; happy to enforce that invariant here if preferred.

[WebSpider]

Thanks for your PR!

The code itself looks good, but can you add the errored API-reply from #631 as a fixture?