Fix remaining feedback and other nits for 2989

[dunxen]

Closes #3170

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.74%. Comparing base (8c1b3d1) to head (016d7e1).

Files	Patch %	Lines
lightning/src/ln/interactivetxs.rs	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3219      +/-   ##
==========================================
+ Coverage   89.69%   89.74%   +0.05%     
==========================================
  Files         122      122              
  Lines      101791   101791              
  Branches   101791   101791              
==========================================
+ Hits        91300    91354      +54     
+ Misses       7791     7755      -36     
+ Partials     2700     2682      -18     

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[TheBlueMatt]

All super straightforward changes, gonna just land this.