chore(test): add tests for invoice check signature

[chenyukang]

we have build_with_sign support for signature to make sure invoice is not modified after generated.

maybe we need to use it for PRC:

fiber/src/rpc/invoice.rs

Line 114 in cc111f8

match invoice_builder.build() {

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.00%. Comparing base (01c7024) to head (627f86c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #225   +/-   ##
=======================================
  Coverage   40.99%   41.00%           
=======================================
  Files          51       51           
  Lines       36761    36761           
=======================================
+ Hits        15072    15073    +1     
+ Misses      21689    21688    -1     

Flag	Coverage Δ
unittests	41.00% <ø> (+<0.01%)	⬆️

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