ci: fix TSAN false positives from FFI memory reuse

Run TSAN tests sequentially to avoid false positives caused by
memory address reuse between parallel tests crossing FFI boundaries.
The x11 C code is thread-safe (stack-allocated state only).

Author: xdustinface

.github/workflows/sanitizer.yml

@@ -65,6 +65,6 @@ jobs:
           RUSTFLAGS: "-Zsanitizer=thread -Cdebuginfo=2"
           TSAN_OPTIONS: "second_deadlock_stack=1"
         run: |
-          # Async/concurrent crates
+          # Async/concurrent crates (single-threaded to avoid false positives from FFI memory reuse)
           cargo +nightly test -Zbuild-std --target x86_64-unknown-linux-gnu \
-            -p dash-spv -p key-wallet --lib --tests
+            -p dash-spv -p key-wallet --lib --tests -- --test-threads=1