Fix uniffi feature breaking postgres/migration integration tests

[juliusjulyp]

Context

cargo test --all-features fails to compile tests/integration_tests_postgres.rs
and tests/integration_tests_migration.rs with type
mismatches (Arc<NodeEntropy> expected, NodeEntropy found; Vec<u8>
expected, [u8; 64] found; Node vs Arc<Node>).

Cause

The uniffi feature changes the public shape of NodeEntropy, Node, and
related builder methods for FFI — wrapping return types in Arc<T>
and switching NodeEntropy::from_seed_bytes to take Vec<u8> instead of a
fixed [u8; 64] array.

Fix

Both files now follow the same #[cfg(feature = "uniffi")] /
#[cfg(not(feature = "uniffi"))] pattern similar
to tests/integration_tests_rust.rs and tests/common/mod.rs

Testing

cargo test --features postgres --test integration_tests_postgres —
3/3 passing, against local Postgres instance

Open to feedback if a different approach is preferred — e.g. expanding CI
coverage to catch this combination going forward, in addition to or instead
of this fix

[ldk-reviews-bot]

I've assigned @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.