Add support for Seg6Local encapsulation type

[Aperence]

This commit provide support for Seg6Local (https://segment-routing.org/, https://www.segment-routing.net/images/201901-SRv6.pdf). By adding this support, it is now possible to create various SRv6 segments with netlink-packet-route.

This commit adds the support for the following segments: End, End.X, End.T, End.B6, End.B6.Encaps, End.DX2, End.DX6, End.DX4, End.DT6, End.DT4, End.DT46.

The following segments are not yet implemented/tested: End.BM, End.S, End.AS, End.AM, End.BPF.

Further support could be added in the future to implement the remaining segments, but this patch should be a good starting point in my opinion by providing the most common segments.

Additional tests are also included by comparing the resulting messages with messaged captured in wireshark.

[codecov]

Codecov Report

❌ Patch coverage is 83.01887% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.02%. Comparing base (1fb4bd7) to head (a84d40d).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
src/route/seg6local.rs	82.11%	27 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   68.10%   69.02%   +0.91%     
==========================================
  Files         144      148       +4     
  Lines       10103    10809     +706     
==========================================
+ Hits         6881     7461     +580     
- Misses       3222     3348     +126     

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[gemini-code-assist]

Code Review

This pull request introduces support for Seg6Local (Segment Routing over IPv6 Local) routing attributes and actions. It adds the seg6local module containing parsing, serialization, and structure definitions for RouteSeg6LocalIpTunnel, Seg6LocalAction, and SRH (Segment Routing Header), along with comprehensive unit tests. Review feedback suggests replacing a todo!() in the serialization path of RouteSeg6LocalIpTunnel::Unspec with an empty block to prevent runtime panics. Additionally, it is recommended to refactor the recursive push_segments and get_segments helper functions in SRH into iterative implementations using standard slice methods, which simplifies the code and avoids unnecessary heap allocations and cloning.

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