feat: Detect incorrect multi-threaded use from c based ffi (microsoft#499)

Add runtime detection for shared handle misuse

wrap the FFI engine handle with parking_lot::RwLock when the new
contention_checks feature is enabled, surfacing a clear “handle is already
in use” error instead of allowing undefined behavior
keep the feature optional so no_std builds or environments that supply
their own synchronization can opt out
caution users that this guards the handle itself but does not make the
engine’s operations globally thread-safe on its own

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

Author: anakrish

.github/workflows/test-ffi.yml

@@ -24,4 +24,5 @@ jobs:
           cargo fetch
           cargo build -r --frozen
           cargo clippy --all-targets --no-deps -- -Dwarnings
+          cargo test --features contention_checks --frozen
         working-directory: ./bindings/ffi