fix: review cargo config

* move package settings into correct table
* move .cargo into wasm dir
* set "std" for burn

wasm/.cargo/config.toml

@@ -0,0 +1,8 @@
+[target.wasm32-unknown-unknown]
+rustflags = [
+    "-Ctarget-feature=+simd128,+bulk-memory,+reference-types",
+    '--cfg', 'getrandom_backend="wasm_js"',
+    "--cfg=has_std",
+    "-Zlocation-detail=none",
+    "-Zthreads=6",
+]