fix(oracle): accept any non-empty BaseAsset/QuoteAsset in OracleSet

[e-desouza]

Why

validate_oracle_currency restricted BaseAsset and QuoteAsset to 3-character ISO codes or 40-character hex strings. The rippled node imposes no such restriction — it accepts any non-empty string for these fields. This caused the Rust SDK to silently reject valid oracle pairs (e.g. BTC, DOGE, AAPL, EURO) that rippled would happily process.

Introduced in #156 (9570a0e).

What changed

• validate_oracle_currency in src/models/transactions/mod.rs: replaced the ISO/hex pattern check with a simple non-empty string check
• Replaced test_invalid_base_asset_rejected (which asserted the old ISO/hex restriction) with:
  • test_arbitrary_non_empty_base_asset_accepted — verifies EURO, BTC, DOGE, AAPL, and other arbitrary codes are accepted
  • test_empty_base_asset_rejected — verifies empty string is still rejected
  • test_empty_quote_asset_rejected — verifies empty string is rejected for quote_asset too

How to validate

cargo test --lib --features std

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.53%. Comparing base (49196f9) to head (6611042).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #335      +/-   ##
==========================================
+ Coverage   84.49%   84.53%   +0.03%     
==========================================
  Files         227      227              
  Lines       24245    24283      +38     
==========================================
+ Hits        20487    20528      +41     
+ Misses       3758     3755       -3     

Flag	Coverage Δ
integration	71.52% <ø> (+0.19%)	⬆️
unit	85.23% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/models/transactions/mod.rs	56.22% <100.00%> (-0.15%)	⬇️
src/models/transactions/oracle_set.rs	93.60% <100.00%> (+0.33%)	⬆️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

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