Add Unit Tests for Packet Filtering

[arya2004]

There are currently no unit tests for the packet filtering logic in model/packet.go. Adding tests will improve reliability and make future changes safer.

Task:

• Create internal/model/packet_test.go
• Add tests for the ApplyFilters function (see sample test in the issue body above)
• Test various filter combinations: protocol, source IP, destination IP, ports, and free text.

Why:
Automated tests help catch bugs early and encourage safe refactoring.

[kaustubhudavant-hash]

@arya2004 please assign this to me for hacktoberfest 2025
Thanks kaustubh