Fix optional translation fields in websocket Error model

[Copilot]

Home Assistant's websocket API doesn't always include translation_key, translation_placeholders, and translation_domain in error responses, but the Error Pydantic model required them — causing a ValidationError on valid server responses like invalid_format errors.

Changes

• homeassistant_api/models/websocket.py: Made translation_key, translation_placeholders, and translation_domain optional (None default) on the Error model
• tests/test_errors.py: Added test_error_model_without_optional_fields to assert Error parses correctly with only code and message

# Before — raises ValidationError when translation fields are absent
class Error(BaseModel):
    code: str
    message: str
    translation_key: str
    translation_placeholders: dict[str, str]
    translation_domain: str

# After
class Error(BaseModel):
    code: str
    message: str
    translation_key: Optional[str] = None
    translation_placeholders: Optional[dict[str, str]] = None
    translation_domain: Optional[str] = None

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Library Bug] error responses do not always contain error.translation_key and related keys.</issue_title>
<issue_description>Describe the bug
Websocket API error responses do not always contain error.translation_key and related keys.

To Reproduce

from homeassistant_api import WebsocketClient

with WebsocketClient(
    'wss://<domain>/api/websocket',
    '<long lived token>'
) as ws_client:
    res_id = ws_client.send("recorder/statistics_during_period",
        start_time="2025-12-30T17:20:00.000Z",
        end_time="2025-12-30T22:20:00.000Z",
        #statistic_ids=["sensor.display_switch_electric_consumption_kwh"],
        #period="hour" # this triggers the server side error because the fields are required.
    )
    resp = ws_client.recv(res_id)
    print(resp)

The server sends this back:

{'id': 2, 'type': 'result', 'success': False, 'error': {'code': 'invalid_format', 'message': "required key not provided @ data['period']. Got None\nrequired key not provided @ data['start_time']. Got None\nrequired key not provided @ data['statistic_ids']. Got None"}}

Resulting in the following output:

pydantic_core._pydantic_core.ValidationError: 3 validation errors for ErrorResponse
error.translation_key
  Field required [type=missing, input_value={'code': 'invalid_format'...tistic_ids']. Got None"}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
error.translation_placeholders
  Field required [type=missing, input_value={'code': 'invalid_format'...tistic_ids']. Got None"}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
error.translation_domain
  Field required [type=missing, input_value={'code': 'invalid_format'...tistic_ids']. Got None"}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing

Expected behavior
A clear and concise description of what you expected to happen.
The errors should be accepted without these keys since clearly they are optional for the server.

Desktop (please complete the following information):

• OS: macOS
• OS Version Sonoma 14.8.1
• HomeAssistantAPI Version: 5.0.2.post2

Workaround

Patch the BaseError model to look like this:

class Error(BaseModel):
    code: str
    message: str
    translation_key: str | None = None
    translation_placeholders: dict[str, str] | None = None
    translation_domain: str | None = None

Proper solution will need some special pydantic magic I assume.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Library Bug] error responses do not always contain error.translation_key and related keys. #221

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.46%. Comparing base (21fecd8) to head (41cc4b6).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #226      +/-   ##
==========================================
+ Coverage   97.45%   97.46%   +0.01%     
==========================================
  Files          25       25              
  Lines        1648     1655       +7     
==========================================
+ Hits         1606     1613       +7     
  Misses         42       42              

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