Add Kaifa MA309M dump from pos-ei-don

[Tomer27cz]

Adds MBUS dump of Kaifa MA309M by @pos-ei-don from this comment

[PolarGoose]

Great job. I like this change :)
If it passes tests then merge it, you should have rights to do so.

[Copilot]

Pull request overview

This PR adds a new Kaifa MA309M M-Bus meter dump fixture (from @pos-ei-don’s ESPHome thread) and registers it in the integration test suite, extending real-world coverage for encrypted General-GLO-Ciphering (0xDB) M-Bus framed payloads.

Changes:

• Add a new expected-fixture header containing the raw frame, decryption key, and expected parsed values for Kaifa MA309M.
• Register a new SUBCASE in the M-Bus integration tests to exercise the parser against this dump.
• Add the corresponding raw dump, key, and decoded XML reference files under tests/dumps/.

Reviewed changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_meter_dumps.cpp	Adds a new M-Bus integration subcase for Kaifa MA309M and sets the decryption key before parsing.
tests/expected/mbus_kaifa_ma309m.h	Introduces the Kaifa MA309M raw frame, key, and expected OBIS outputs for the test.
tests/dumps/mbus_kaifa_ma309m.log	Adds the raw hex dump used to generate the fixture.
tests/dumps/mbus_kaifa_ma309m.key	Adds the (throwaway) AES-GCM decryption key associated with the dump.
tests/dumps/mbus_kaifa_ma309m_decoded.xml	Adds a decoded reference view of the payload to aid validation/debugging.

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