fix shelly phase iteration

[LKuemmel]

Es gibt normal dreiphasige Shellys (Shelly EM) die dann weniger Phasen haben, aber auch Shellys bei denen noch andere Werte im meters-JSON sind.

basiert auf #3132

[Copilot]

Pull request overview

This PR fixes a phase iteration bug in the Shelly device integration. Some Shelly devices (e.g., Shelly EM) may return fewer than 3 phases, while others can return extra entries in their meters/emeters JSON arrays beyond the expected 3 phases (e.g., Shelly 3EM-63 Gen3). The old code iterated over all entries unconditionally, which caused either index-out-of-range errors or incorrect data assignment. The fix caps iteration at 3 and also refactors local ['a', 'b', 'c'] lists into a shared constants.py.

Changes:

• Introduced constants.py with a shared ALPHABETICAL_INDEX constant to replace repeated local ['a', 'b', 'c'] lists in bat.py, counter.py, and inverter.py.
• Changed for i in range(len(meters)) to for i in range(0, min(3, len(meters))) in all three component files for Gen 1 meter types, preventing out-of-bounds list access when more than 3 meters are present.
• Replaced guarded conditional expressions (x if key else 0) with .get(key, 0) for cleaner and safer dict access across all three component files.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
constants.py	New file introducing shared ALPHABETICAL_INDEX constant
bat.py	Applies iteration cap, uses .get() for safe field access, and moves power = 0 inside the try block
counter.py	Applies iteration cap, uses .get() for safe field access, and uses .get() for total_act_power
inverter.py	Applies iteration cap, uses .get() for safe field access, but still uses direct key access for total_act_power on line 69

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[Copilot]

The PR description and referenced issue state that the bug occurs with devices that have more than 3 entries in their meters or emeters array (e.g., Shelly 3EM-63 Gen3 which may include extra non-phase entries). The core fix — capping iteration at 3 with min(3, len(meters)) — is not covered by any new test case. Given that the test file (shelly_test.py) has comprehensive parametrized test cases for all existing device types and scenarios, a test case using a meters/emeters list with more than 3 items would be needed to verify the fix and prevent regressions.