fix(ci): rebuild cdylib with ffi feature before FFI tests [PECOBLR-2086] (#365)

## Summary
- Fixes CI failure where `cargo test --features ffi` fails with
"undefined symbol: AdbcDriverInit" when run after `cargo test` (without
ffi feature)
- Adds `cargo build --locked --features ffi` before the FFI test step to
force a cdylib rebuild with the correct symbols
- Root cause: Cargo doesn't always rebuild the cdylib target when only
feature flags change in incremental builds

## Test plan
- [ ] CI passes: `cargo test --locked` followed by `cargo test --locked
--features ffi` both succeed
- [ ] Verify with `nm -D target/debug/libdatabricks_adbc.so | grep
AdbcDriverInit` that the symbol is present after the build step

This pull request was AI-assisted by Isaac.

Author: vikrantpuppala

.github/workflows/rust_test.yaml

@@ -173,6 +173,7 @@ jobs:
           fi
 
           cargo test --locked
+          cargo build --locked --features ffi
           cargo test --locked --features ffi
 
           if [[ -f ci/scripts/post-test.sh ]]; then