Fix older firmware in battery 'zero' mode treated as standby due to missing permissions

[DCSBL]

Before:

# API 2.1.0
Batteries.from_json("{\"mode\": \"zero\"}") → “standby” -- WRONG
Batteries.from_json("{\"mode\": \"standby\"}”) → “standby”

# API 2.2.0
Batteries.from_json("{\"mode\": \"zero\", \"permissions\": [\"charge_allowed\", \"discharge_allowed\"]}”) → “zero"
Batteries.from_json("{\"mode\": \"standby\", \"permissions\": []}”) → “standby”

After:

# API 2.1.0
Batteries.from_json("{\"mode\": \"zero\"}") → “zero” -- FIXED
Batteries.from_json("{\"mode\": \"standby\"}”) → “standby”

# API 2.2.0
Batteries.from_json("{\"mode\": \"zero\", \"permissions\": [\"charge_allowed\", \"discharge_allowed\"]}”) → “zero"
Batteries.from_json("{\"mode\": \"standby\", \"permissions\": []}”) → “standby”

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.26%. Comparing base (824bdf9) to head (b4f0ed1).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
homewizard_energy/models.py	92.85%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #587   +/-   ##
=======================================
  Coverage   99.26%   99.26%           
=======================================
  Files           9        9           
  Lines         679      682    +3     
  Branches       62       63    +1     
=======================================
+ Hits          674      677    +3     
  Misses          2        2           
  Partials        3        3           

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[Copilot]

Pull request overview

This PR fixes a bug where older firmware (API 2.1.0) in battery 'zero' mode was incorrectly treated as 'standby' due to the missing permissions field. The fix distinguishes between a missing permissions field (older firmware) and an explicitly empty permissions array (intentional standby mode).

Key changes:

• Made the permissions field nullable to distinguish between missing and empty
• Added backwards compatibility logic to preserve 'zero' mode when permissions field is absent
• Added test fixtures for both API versions (2.1.0 without permissions, 2.2.0 with permissions)

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
homewizard_energy/models.py	Changed permissions field to nullable, updated deserialization logic, and added backwards compatibility in post_deserialize to keep mode as ZERO when permissions is None
tests/v2/test_v2_batteries.py	Updated test parametrization to test both API 2.1.0 and 2.2.0 fixtures for HWE-P1 model
tests/v2/fixtures/HWE-P1/batteries_2_1_0.json	Added fixture for API 2.1.0 (older firmware) with mode="zero" but no permissions field
tests/v2/fixtures/HWE-P1/batteries_2_2_0.json	Added fixture for API 2.2.0 (newer firmware) with mode="zero" and permissions field
tests/v2/snapshots/test_v2_batteries.ambr	Updated snapshots to reflect expected behavior for both API versions

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