feat: hysteresis for the display heater control

[maxirmx]

No description provided.

[Copilot]

Pull request overview

Adds hysteresis to the display heater relay control by splitting the single relay threshold into distinct “on” and “off” thresholds, reducing relay chatter around the activation point while keeping prior behavior for read failures and shutdown safety.

Changes:

• Introduces separate relay on/off thresholds (with validation) and updates the control logic to apply hysteresis.
• Updates unit tests to validate hysteresis behavior and invalid-threshold rejection.
• Updates hardware documentation/config naming and bumps the project version.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/peripherals/temperature_sensor.cpp	Implements hysteresis relay control, validates on/off thresholds, and logs configured thresholds during initialization.
include/peripherals/temperature_sensor.h	Updates constructor API to accept on/off thresholds and stores them as members with defaults for the callback-based constructor.
include/hardware/hardware_config.h	Replaces the single relay threshold constant with on/off threshold constants.
tests/temperature_sensor_test.cpp	Replaces the no-hysteresis relay test with a hysteresis behavior test and adds invalid-threshold coverage.
docs/hardware.md	Updates configuration docs and explains the new hysteresis behavior for the display heater relay.
CMakeLists.txt	Bumps the project version to 0.3.4.

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