CI: Speed up test-driver-rust build

On my machine more than a minute is spent on running build.rs for test-driver-rust generating slint code for all the .slint files, as the build-time feature is enabled.

This patch builds the build script with optimizations, to reduce the time spent on generating code. On my machine that cuts it down to ~30 seconds.

Author: tronical

.github/workflows/build_and_test_reusable.yaml

@@ -49,6 +49,8 @@ jobs:
             QT_QPA_PLATFORM: offscreen
             RUSTFLAGS: -D warnings
             CARGO_PROFILE_DEV_DEBUG: 0
+            # Build slint-compiler in release to make test-driver-rust's build-time feature build faster.
+            CARGO_PROFILE_DEV_BUILD_OVERRIDE_OPT_LEVEL: 3
             CARGO_INCREMENTAL: false
             RUST_BACKTRACE: 1
             SLINT_EMIT_DEBUG_INFO: 1