add support for end-of-RIB message test

[digizeph]

This partially addresses #137.

[codecov]

Codecov Report

Merging #138 (312327b) into main (0876066) will increase coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #138      +/-   ##
==========================================
+ Coverage   63.35%   63.57%   +0.22%     
==========================================
  Files          68       68              
  Lines        6116     6131      +15     
==========================================
+ Hits         3875     3898      +23     
+ Misses       2241     2233       -8     

Files	Coverage Δ
src/lib.rs	22.03% <ø> (ø)
src/models/bgp/attributes/mod.rs	13.37% <100.00%> (+2.67%)	⬆️
src/parser/bgp/messages.rs	65.36% <100.00%> (+2.40%)	⬆️