Fix just clean command for Windows compatibility and missing directory handling

Co-authored-by: simongdavies <1397489+simongdavies@users.noreply.github.com>

Author: Copilot

Justfile

@@ -60,8 +60,8 @@ clean-rust:
     cd src/tests/rust_guests/simpleguest && cargo clean
     cd src/tests/rust_guests/dummyguest && cargo clean
     cd src/tests/rust_guests/callbackguest && cargo clean
-    cd src/tests/rust_guests/witguest && cargo clean
-    cd src/tests/rust_guests/witguest && rm -f interface.wasm
+    {{ if os() == "windows" { "if (Test-Path src/tests/rust_guests/witguest) { cd src/tests/rust_guests/witguest; cargo clean }" } else { "[ -d src/tests/rust_guests/witguest ] && cd src/tests/rust_guests/witguest && cargo clean || true" } }}
+    {{ if os() == "windows" { "if (Test-Path src/tests/rust_guests/witguest/interface.wasm) { Remove-Item src/tests/rust_guests/witguest/interface.wasm }" } else { "rm -f src/tests/rust_guests/witguest/interface.wasm" } }}
     git clean -fdx src/tests/c_guests/bin src/tests/rust_guests/bin
 
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