fix a bug where as4path not used when same length

[digizeph]

This pull request includes changes to the src/models/bgp/attributes/aspath.rs file to handle different sequence lengths in AS path merging and to add new test cases for these scenarios. The most important changes are:

Handling Different Sequence Lengths:

• Modified impl AsPath to handle cases where diff_len is zero or negative, ensuring the correct AS path sequence is used. (src/models/bgp/attributes/aspath.rs, src/models/bgp/attributes/aspath.rsL639-R642)

Adding Test Cases:

• Added new test cases to verify the behavior when the sequence length is the same, ensuring the as4path is used in such scenarios. (src/models/bgp/attributes/aspath.rs, src/models/bgp/attributes/aspath.rsR1003-R1008)

[codecov]

Codecov Report

Attention: Patch coverage is 95.65217% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.79%. Comparing base (59f05f0) to head (1aa8fd4).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/parser/bmp/messages/route_mirroring.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #187      +/-   ##
==========================================
+ Coverage   92.77%   92.79%   +0.01%     
==========================================
  Files          70       70              
  Lines        8351     8369      +18     
==========================================
+ Hits         7748     7766      +18     
  Misses        603      603              

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