feat(systemd): add robust resume service for sensor re-initialization

[sidneijp]

This PR adds a dedicated python3-validity-resume.service to address the common issue where the fingerprint sensor fails to re-initialize after suspend on devices like the ThinkPad T480.

Motivation

The existing open-fprintd-resume.service often fails due to a race condition with D-Bus proxy initialization.

Changes

• Added debian/python3-validity-resume.service which restarts python3-validity and open-fprintd on resume.
• Includes a D-Bus 'readiness gate' via ExecStartPost to ensure the driver is responsive before the service is marked finished.
• Eliminates the need for arbitrary sleep delays or PAM-based hacks.
• Packaging: The file name follows the [package]-[name].service convention, ensuring it is automatically detected, installed, and enabled by dh_installsystemd during the package build process.

Resolves #254.