Disable wat feature from wasmer and wasmtime (#2586)

* Enable `wasmer` dependency to run tests

Instead of only running the tests if the feature is enabled. Also enable
the `wat` feature in preparation to remove the `sys-default` feature.

* Disable `sys-default` feature

It doesn't seem to be needed.

* Disable more `wasmer` features

Disable the default features on `wasmer-compiler-singlepass`.

* Disable `wasmtime`'s default features

Only enable the ones that are needed.

Cargo.toml

@@ -162,9 +162,9 @@ wasm-encoder = "0.24.1"
 wasm-instrument = "0.4.0"
 wasm_thread = "0.3.0"
 wasmer = { package = "linera-wasmer", version = "4.3.6-linera.4", default-features = false }
-wasmer-compiler-singlepass = { package = "linera-wasmer-compiler-singlepass", version = "4.3.6-linera.4" }
+wasmer-compiler-singlepass = { package = "linera-wasmer-compiler-singlepass", version = "4.3.6-linera.4", default-features = false }
 wasmparser = "0.101.1"
-wasmtime = "25.0.0"
+wasmtime = { version = "25.0.0", default-features = false, features = ["cranelift", "runtime", "std"] }
 wasmtimer = "0.2.0"
 webassembly-test = "0.1.0"
 web-sys = "0.3.69"