Fix Luckfox GPIO chip resolution and button init races

[3rdIteration]

Summary

• resolve global GPIO line selectors to real /dev/gpiochipN device nodes on Luckfox systems where /sys/class/gpio chip names are base-numbered
• make HardwareButtons.get_instance() thread-safe and exception-safe to avoid partial singleton state
• add fallback behavior for bias open failures and improve startup resilience
• add targeted tests covering resolver mapping, fallback mapping, failed init cleanup, and concurrent singleton initialization

Problem

Merging GPIO portability changes caused regressions on Luckfox Pico Mini:

• attempts to open invalid chip paths like /dev/gpiochip32
• poisoned HardwareButtons singleton state after init exceptions
• startup races where multiple threads initialize button GPIO simultaneously
• KEY2 line conflicts surfacing as Errno 16 when line ownership is contested

Validation

• pytest -q tests/test_buttons_gpio_resolution.py (new tests)
• pytest -q tests/test_io_config_profiles.py
• device verification on Luckfox Pico Mini with line-number io_config mapping