refactor(whatsrust): remove residual facade test copies

[Andiveli]

Summary

• Complete the Rust facade cleanup by removing duplicate tests from lib.rs.
• Preserve the tests in facade_tests.rs and keep explicit public reexports.

Chain Context

• Immediate parent: PR refactor(whatsrust): stage facade test ownership #333.
• Diagram: refactor(whatsrust): extract group and chat queries #327 -> refactor(whatsrust): relocate forwarding result types #332 -> refactor(whatsrust): stage facade test ownership #333 -> 📍 this PR.
• End: lib.rs is a 70–120 line public facade with no unsafe, locks, ABI structs, callbacks, endpoints, or query/send policy.

Testing

• cargo fmt --all -- --check
• CARGO_TARGET_DIR=/home/samael/Escritorio/public/wptui-public/target cargo check --workspace --all-targets
• CARGO_TARGET_DIR=/home/samael/Escritorio/public/wptui-public/target cargo test -p whatsrust --lib -- --test-threads=1
• git diff --check

Review Budget and Rollback

• Authored diff: 226 lines (4 additions + 222 deletions).
• Rollback: revert commit 7a4d8b1.

Closes #334