[sBTC DR] Add test for txid

[friedger]

Description

This PR

• adds a test that shows txids are passed correctly to the contract
• see Romeo should pass the unreversed txid to asset contract #164

[codecov]

Codecov Report

Merging #184 (b9d9dd1) into main (937456c) will increase coverage by 1.51%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   38.01%   39.53%   +1.51%     
==========================================
  Files          40       44       +4     
  Lines        4714     4872     +158     
  Branches        0       28      +28     
==========================================
+ Hits         1792     1926     +134     
- Misses       2922     2944      +22     
- Partials        0        2       +2     

Flag	Coverage Δ
unittests	84.71% <ø> (?)

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Files	Coverage Δ
romeo/src/proof_data.rs	98.70% <100.00%> (+<0.01%)	⬆️

... and 4 files with indirect coverage changes

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