Improve API of how client should use our library

[PolarGoose]

It is an attempt to elegantly solve #4.
I propose having a single callback that returns the entire AxdrCapture object, which includes methods to retrieve a string or float value if needed.
Also, I pass this callback into a constructor. It is better. It reduces potential dynamic memory allocations and aligns with how we use our library in EspHome.

[Copilot]

Pull request overview

This PR updates the library’s public parsing API to use a single per-parser callback that receives the full AxdrCapture, enabling callers to choose how to interpret OBIS/value data (including preserving precision) and avoiding per-parse callback plumbing. It also consolidates logging into utils.h and updates tools/tests to the new API.

Changes:

• Replace the “cooked” callback signature with DlmsDataCallback(std::function<void(const AxdrCapture&)>) and pass it via DlmsParser/AxdrParser constructors; simplify parse() to only take the buffer.
• Introduce AxdrCapture helper methods (obis_as_string, value_as_string, value_as_float_with_scaler_applied, etc.) and remove older utility conversion helpers from utils.
• Refactor logging: move Logger/LogLevel from log.h into utils.h and update call sites; add a shared test log fixture.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tools/decode_readout.cpp	Updated CLI tool to use constructor-injected AxdrCapture callback and parse(data) API.
tests/test_util.h	Adds shared log fixture for tests; used across multiple test files.
tests/test_utils.cpp	Updates to TEST_CASE_FIXTURE and removes tests tied to removed utils helpers.
tests/test_meter_dumps.cpp	Updates integration tests to new parser callback + parse() signature.
tests/test_mbus_decoder.cpp	Switches to fixture-based tests (logging setup).
tests/test_hdlc_decoder.cpp	Switches to fixture-based tests (logging setup).
tests/test_example.cpp	Updates example usage to new callback/constructor and parse() API.
tests/test_axdr_registry.cpp	Updates AxdrParser construction to require callback.
src/dlms_parser/utils.h / utils.cpp	Moves logger into utils.h; removes old float/string/OBIS/hex formatting helpers.
src/dlms_parser/axdr_parser.h / axdr_parser.cpp	Renames capture type to AxdrCapture, adds helper methods, stores callback as member, and emits via member callback.
src/dlms_parser/dlms_parser.h / dlms_parser.cpp	Requires callback in constructor; parse() no longer accepts callback argument.
src/dlms_parser/log.h	Deleted (logging moved into utils.h).
src/dlms_parser/{hdlc_decoder,mbus_decoder,apdu_handler}.cpp	Update includes from log.h to utils.h.
src/dlms_parser/decryption/*	Drops log.h include (now provided via utils.h).

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