Add Stellar Soroban property tests

[kaycke1337]

Summary

• Add proptest integration coverage for all four Stellar Soroban crates
• Cover announcer events, registry round trips and validation, sender transfer/batch invariants, and Wraith Names lifecycle behavior
• Document property-test commands and add a scheduled nightly CI job with 16,384 cases

Closes #5

Validation

• cargo fmt --all --check
• cargo test --workspace --test properties
• cargo test --workspace
• git diff --check

[truthixify]

Heads up — we've just set up a develop branch as the integration target for all Drips × Stellar Wave contributions, and I've retargeted this PR's base from main to develop on your behalf. The diff is unchanged; nothing to do on your end.

Going forward, please branch from and target develop. We'll periodically merge develop → main as we cut releases. Thanks for contributing!

[truthixify]

Merging this in — really clean implementation. Dedicated tests/properties.rs per crate, the WRAITH_PROPTEST_CASES env knob with a sensible 1024 default, and the nightly CI job at 16k cases all match the spec. The name-grammar strategies in wraith-names properties were a nice touch.

Thanks @kaycke1337 — first PR through the develop branch.