fix: Add get_port_by_mac for DellOS9

[rafalglx]

This pull request adds new functionality to the Dell OS9 switch management module by introducing a method to retrieve the port name associated with a given MAC address, along with comprehensive unit tests to ensure its reliability. The changes enhance both the feature set and the test coverage of the codebase.

New Feature: Port Lookup by MAC Address

• Added the get_port_by_mac method to the DellOS9 class in dell_os9/base.py, which retrieves the port name for a specified MAC address, including error handling for invalid or unknown MACs.

Testing Enhancements

• Created new unit tests in test_base.py to verify the behavior of get_port_by_mac, covering successful lookup, MAC address not found, and invalid MAC address scenarios.

[Copilot]

Pull Request Overview

This PR implements the get_port_by_mac method for DellOS9 switch management to resolve issue #4. The implementation allows querying the switch's MAC address table to find which port a specific MAC address is connected to.

• Adds get_port_by_mac method to DellOS9 base class with MAC validation and port lookup functionality
• Includes comprehensive test coverage for successful lookups, not found cases, and invalid MAC addresses
• Uses regex pattern matching to parse the switch's MAC address table output

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
mfd_switchmanagement/vendors/dell/dell_os9/base.py	Implements get_port_by_mac method with MAC validation and switch command execution
tests/unit/test_mfd_switchmanagement/test_vendors/test_dell/test_dell_os9/test_base.py	Adds comprehensive test suite covering success, failure, and validation scenarios

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