Chore/fix clippy perf warnings

[ASuciuX]

Description

Replaces expect_fun_call with unwrap_or_else.

Applicable issues

• fixes Fix Clippy perf for stacks-signer  #4566

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 71.72%. Comparing base (80adc27) to head (497fec3).

Additional details and impacted files

@@             Coverage Diff             @@
##             next    #4567       +/-   ##
===========================================
- Coverage   83.35%   71.72%   -11.64%     
===========================================
  Files         453      453               
  Lines      328491   328491               
  Branches      323      323               
===========================================
- Hits       273822   235616    -38206     
- Misses      54661    92867    +38206     
  Partials        8        8               

Files	Coverage Δ
stacks-signer/src/signer.rs	74.79% <83.33%> (-0.48%)	⬇️

... and 233 files with indirect coverage changes

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