added stdin support for topos

[hellt]

fix #1598

[codecov]

Codecov Report

Merging #1621 (2a7d29a) into main (0cb7612) will decrease coverage by 0.07%.
The diff coverage is 43.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1621      +/-   ##
==========================================
- Coverage   49.07%   49.01%   -0.07%     
==========================================
  Files         135      135              
  Lines       13061    13083      +22     
==========================================
+ Hits         6410     6412       +2     
- Misses       5946     5966      +20     
  Partials      705      705              

Files	Coverage Δ
clab/config.go	66.83% <100.00%> (-0.09%)	⬇️
types/topo_paths.go	69.91% <100.00%> (+0.54%)	⬆️
clab/clab.go	74.74% <37.03%> (-2.49%)	⬇️

... and 2 files with indirect coverage changes