Add generic IPv4/IPv6 packet parsing support to IpRepr

[jeff-moon]

• Add generic Packet type for handling both IPv4 and IPv6 packets
• Add parsing functionality for protocol-agnostic IP packet handling
• Add tests for new parsing functionality

This also adds ChecksumCapabilities into the generic parse, since it's needed by IPv4, which is something that I am (and probably you will be) iffy about. This would clean up a lot of our code that generically handles IPv4/IPv6 code.

[codecov]

Codecov Report

❌ Patch coverage is 97.22222% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.41%. Comparing base (cfbfeae) to head (bfa5150).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/wire/ip.rs	97.22%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1087      +/-   ##
==========================================
+ Coverage   80.34%   80.41%   +0.07%     
==========================================
  Files          81       81              
  Lines       24335    24443     +108     
==========================================
+ Hits        19552    19657     +105     
- Misses       4783     4786       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[thvdveld]

I don't think it's that iffy. Looks fine to me!