add I2C and SPI tools for hardware interaction (#140)

* add I2C and SPI tools for hardware interaction

- Implemented I2CTool for I2C bus interaction, including device scanning, reading, and writing.
- Implemented SPITool for SPI bus communication, supporting device listing, data transfer, and reading.
- Added platform-specific implementations for Linux and stubs for non-Linux platforms.
- Updated agent loop to register new I2C and SPI tools.
- Created documentation for hardware skills, including usage examples and pinmux setup instructions.

* Remove build constraints for Linux from I2C and SPI tool files.

pkg/tools/spi_other.go

@@ -0,0 +1,13 @@
+//go:build !linux
+
+package tools
+
+// transfer is a stub for non-Linux platforms.
+func (t *SPITool) transfer(args map[string]interface{}) *ToolResult {
+	return ErrorResult("SPI is only supported on Linux")
+}
+
+// readDevice is a stub for non-Linux platforms.
+func (t *SPITool) readDevice(args map[string]interface{}) *ToolResult {
+	return ErrorResult("SPI is only supported on Linux")
+}