share/befp: rework collecting and verifying the BEFP

[vgonkivs]

Overview

• Use an orthogonal axis to collect and verify BEFP instead of collecting and verifying it against a single Merkle Root(where ErrByzantine occurred)
• collect only 1/2 of the shares instead of all available shares from the row/col

Checklist

• New and updated code has appropriate documentation
• New and updated code has new and/or updated testing
• Required CI checks are passing
• Visual proof for any user facing features like CLI or documentation updates
• Linked issues closed with keywords

[codecov-commenter]

Codecov Report

Merging #2408 (d8ce446) into main (387c160) will decrease coverage by 0.20%.
The diff coverage is 61.42%.

@@            Coverage Diff             @@
##             main    #2408      +/-   ##
==========================================
- Coverage   53.25%   53.05%   -0.20%     
==========================================
  Files         156      156              
  Lines        9915     9946      +31     
==========================================
- Hits         5280     5277       -3     
- Misses       4180     4211      +31     
- Partials      455      458       +3     

Impacted Files	Coverage Δ
share/eds/byzantine/bad_encoding.go	35.65% <30.76%> (-1.05%)	⬇️
share/eds/byzantine/share_proof.go	50.00% <60.00%> (ø)
share/eds/byzantine/byzantine.go	73.33% <89.65%> (+11.79%)	⬆️

... and 5 files with indirect coverage changes

[Wondertan]

LGTM

[adlerjohn]

looks ok.