Remove dependency on external shell scripts for GPIO control

[ajlennon]

Problem

The Rust application currently depends on external shell scripts (xm125-control.sh and xm125-firmware-flash.sh) for GPIO control and firmware management operations. This creates several issues:

Current Dependencies

• /usr/bin/xm125-control.sh - Required for bootloader mode switching and GPIO control
• /usr/bin/xm125-firmware-flash.sh - Required for firmware flashing operations
• stm32flash external binary - Required for actual firmware programming

Issues with Current Approach

1. Deployment Complexity: Requires coordinating multiple files and ensuring correct installation paths
2. Error Prone: Script availability, permissions, and path issues can cause failures
3. Maintenance Overhead: Need to maintain both Rust code and shell scripts in sync
4. Platform Dependency: Shell scripts may not work consistently across different embedded Linux distributions
5. Security Concerns: External script execution introduces potential security vectors
6. Testing Complexity: Harder to unit test functionality that depends on external scripts

Proposed Solution

Phase 1: Direct GPIO Control

• Implement native Rust GPIO control using libgpiod or similar crate
• Replace shell script calls with direct GPIO manipulation
• Add proper error handling and validation

Phase 2: Native Firmware Management

• Implement I2C-based firmware flashing directly in Rust
• Remove dependency on stm32flash where possible
• Add firmware verification and integrity checking

Phase 3: Cleanup

• Remove shell script dependencies from Yocto recipe
• Update documentation and deployment guides
• Add comprehensive testing for native implementations

Benefits

• Simplified Deployment: Single binary with all functionality
• Better Error Handling: Native Rust error types and messages
• Improved Testing: Unit testable GPIO and firmware operations
• Cross-Platform: Works consistently across different Linux distributions
• Security: No external script execution
• Performance: Direct system calls instead of shell process spawning

Implementation Notes

• Maintain backward compatibility during transition
• Add feature flags to switch between script-based and native implementations
• Ensure proper privilege handling for GPIO and I2C operations
• Add comprehensive documentation for GPIO pin mappings and hardware requirements

Acceptance Criteria

• Native GPIO control implementation
• Native firmware flashing (where feasible)
• Remove all shell script dependencies
• Maintain full functionality parity
• Add comprehensive tests
• Update documentation

Priority

High - This affects deployment reliability and maintenance overhead