Fix retrieve tapret proof

[crisdut]

Description

This PR intent fix retrieves TapRet Proof from PSBT proprietary.

MISC
Furthermore, it is possible to ask a question that is not directly related to PR:

How do I determine the maximum size of a strict_serialized operation?

For example, how do I know that in tapret_proof, I use U16 instead of U24?

Thanks

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 0.0%. Comparing base (2e3c1d1) to head (7758c44).
Report is 5 commits behind head on master.

Files	Patch %	Lines
psbt/src/csval/tapret.rs	0.0%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##           master    #30   +/-   ##
=====================================
  Coverage     0.0%   0.0%           
=====================================
  Files          18     18           
  Lines        3191   3228   +37     
=====================================
- Misses       3191   3228   +37     

Flag	Coverage Δ
rust	0.0% <0.0%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

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

[dr-orlovsky]

ACK 7758c44

[dr-orlovsky]

@zoedberg @nicbus do you have any idea how we got the tests passing with this bug in place?

[crisdut]

@zoedberg @nicbus do you have any idea how we got the tests passing with this bug in place?

It's because we don't use this method on any calls. I realized this because I'm implementing the PSBT fascia export method. I have other improvements to make involving bp-std and RGB, but I need this one merged first.

PS: None of the other improvements are fixies but instead new methods.