Add invoice_data function to C FFI bindings

[cakesoft-shashank]

This PR adds new extern C function rgblib_invoice_data, to the C FFI bindings, allowing for the retrieval of invoice data from a given invoice string.

[zoedberg]

Thank you! Could you please rebase this on top of the updated master (commit 5c42b9f)?

[cakesoft-shashank]

@zoedberg Done.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.02%. Comparing base (5c42b9f) to head (36fd57f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #72   +/-   ##
=======================================
  Coverage   95.02%   95.02%           
=======================================
  Files          22       22           
  Lines       11390    11390           
=======================================
  Hits        10823    10823           
  Misses        567      567           

Flag	Coverage Δ
rust	95.02% <ø> (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.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.