github: Build the Windows CI job with the MSVC toolchain

The Windows job's `cargo build -p libsql --all-features` was being built
with the `x86_64-pc-windows-gnu` toolchain (MinGW/GCC), set as the default
host triple by `hecrj/setup-rust-action@v2`. MSVC was never exercised. So
breaks that only fail under MSVC -- like the SQLite 3.47.0 `#warning` that
errors with C1021 -- compiled green here. We discovered the gap when
libsql-js (which builds with `--target x86_64-pc-windows-msvc`) failed
downstream on the same code.

Add `--target x86_64-pc-windows-msvc --release` so the Windows job
actually compiles the bundled SQLite encryption amalgamation (sqlite3mc)
with MSVC, and breaks surface in CI.

`cargo clean -p libsql-ffi` runs first so sqlite3mc is rebuilt from source
rather than restored from a cached target/.