fix: Onion v3 parse/format order and render lowercase

[erickcestari]

After running differential fuzzing on the parsing of init Lightning messages between c-lightning and rust-lightning, I found that rust-lightning parses and displays OnionV3 addresses incorrectly.

Tor v3 addresses are base32 of 35 bytes laid out as:
[32-byte ed25519 pubkey][2-byte checksum big-endian][1-byte version]

see: https://spec.torproject.org/rend-spec/encoding-onion-addresses.html

• Parsing now slices 0..32 = pubkey, 32..34 = checksum (BE), 34 = version.
• Display now appends pubkey + checksum + version and lowercases base32.
• Adds/updates test vector accordingly.

[ldk-reviews-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.61%. Comparing base (cd85a80) to head (f9fc879).
⚠️ Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/msgs.rs	90.90%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4090      +/-   ##
==========================================
+ Coverage   88.60%   88.61%   +0.01%     
==========================================
  Files         176      176              
  Lines      132070   132130      +60     
  Branches   132070   132130      +60     
==========================================
+ Hits       117015   117082      +67     
+ Misses      12386    12378       -8     
- Partials     2669     2670       +1     

Flag	Coverage Δ
fuzzing	21.92% <0.00%> (-0.02%)	⬇️
tests	88.44% <90.90%> (+0.01%)	⬆️

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[wpaulino]

Thanks! LGTM.

Could be worth extending the test to do a round-trip on the string to parsed address back to string -- this would've caught the uppercase issue. Could also add an assert on the version to be the default (3).

[ldk-reviews-bot]

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[erickcestari]

Thanks! LGTM.

Could be worth extending the test to do a round-trip on the string to parsed address back to string -- this would've caught the uppercase issue. Could also add an assert on the version to be the default (3).

Updated!

[ldk-reviews-bot]

🔔 1st Reminder

Hey @wpaulino! This PR has been waiting for your review.
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[tnull]

LGTM