Add EMEA charge-schedule support (read from v3 status, write via v2 CPPLUS)

[815rx1]

Summary

EMEA EVs such as the Fiat New 500e do not use the North-American
/v4/accounts/{uid}/vehicles/{vin}/ev/schedule/ endpoint. That endpoint
returns HTTP 500 for these cars. Instead:

• Read: the (up to three) charge schedules are already present inline in
  the v3 vehicle status under evInfo.schedules. No extra request is needed.
• Write: schedules are set with a POST /v2/.../ev/schedule/ carrying a
  CPPLUS command envelope ({command, pinAuth, schedules[]}).

This PR adds a typed representation of those schedules to Vehicle, parses
them from the v3 status, and adds read-modify-write support via a new
Client.set_charge_schedule_emea() / API.set_charge_schedule_emea().

Everything is additive - no existing behaviour changes, the NA
set_charge_schedule (v4) path is untouched.

Confirmed working

Verified live against a 2022 Fiat New 500e (soldRegion=EMEA, sdp=IGNITE,
market=DE, service CPPLUS serviceEnabled=true):

GET  /v4/.../ev/schedule/  -> HTTP 500 Internal Server Error   (NA endpoint, unusable)
POST /v2/.../ev/schedule/  -> HTTP 200
     {"command":"CPPLUS","correlationId":"...","responseStatus":"pending","asyncRespTimeout":2}

Setting slot 1 to "Mon-Fri 01:00-05:00" was reflected both in the subsequent
v3 status read and in the official Fiat app; disabling it again worked the
same way. ChargeSchedule.to_api() reproduces the confirmed 200 payload
byte-for-byte (verified in a unit test against the real status payload).

Fixes the read/write gap reported downstream in hass-uconnect#110
(Fiat 500e EU/EMEA schedule charging).

Changes

client.py

• New @dataclass_json classes ScheduledDays and ChargeSchedule with
  from_api() / to_api() converters (API <-> snake_case).
• New field Vehicle.charge_schedules: list[ChargeSchedule].
• _update_vehicle() now parses evInfo.schedules into that field.
• Client.set_charge_schedule_emea(vin, schedules, verify=False) - takes the
  full slot list, serialises, POSTs, optionally polls the correlation id.
• CHARGING_LEVELS extended with LEVEL_4/LEVEL_5 and the EMEA word-form
  keys LEVEL_ONE..LEVEL_FIVE.
• charging_level_preference is now mapped through CHARGING_LEVELS to an
  int (1..5) instead of being left as the raw string, matching the README
  example ("charging_level_preference": 5) and charging_level. Type hint
  changed str -> int.

api.py

• API.set_charge_schedule_emea(vin, schedules) - the
  POST /v2/.../ev/schedule/ with the CPPLUS envelope. Raises on missing
  correlationId, mirroring the existing set_charge_schedule.

Important behavioural note (documented in the docstring)

The backend replaces the entire schedule list on every write. Sending a
single slot silently resets the others to defaults. Callers must therefore
read vehicle.charge_schedules, modify the slot(s) they need, and pass the
whole list back - set_charge_schedule_emea is designed around exactly this
read-modify-write pattern.

Possible breaking change to flag for the maintainer

charging_level_preference changes type from str ("LEVEL_FIVE") to
int (5). This matches the documented README output and charging_level,
but any downstream consumer comparing the raw string would need updating.
Happy to keep it as a string if you prefer - just say the word.

Not included / out of scope

• Trip history: on this vehicle ECOCOACHING20/TRIPREPORT are
  serviceEnabled=false, the eco-coaching endpoints return nothing usable.
• Auto-detecting NA vs EMEA: left to the caller for now (the two write paths
  coexist). A follow-up could switch on soldRegion.