Define TDX-specific error types

[marcelamelara]

Currently errors are only defined at the entire library-level, but we should add more specific types for some of the sub-modules, like TDX:

#[derive(Debug, Error)]
pub enum TdxDeviceError {
    #[error("Device not found: {0}")]
    DeviceNotFound(String),
    
    #[error("Device not accessible: {0}")]
    DeviceNotAccessible(String),
    
    #[error("Invalid device type: {0}")]
    InvalidDeviceType(String),
    
    #[error("Device operation failed: {0}")]
    OperationFailed(String),
}

Originally posted by @sandlbn in #1 (comment)