AVRO-3800: [Rust] profile section should be declared in the root package

[sarutak]

AVRO-3800

What is the purpose of the change

This PR fixes an issue that [profile.release] declared in wasm-demo/Cargo.toml is ignored.
In that section, opt-level = "s" is specified but it's ignored.

$ cargo test -v --test demos --release
...
     Running `rustc --crate-name hello_wasm ... opt-level=3 ...`
     Running `rustc --crate-name demos ... opt-level=3 ...`

To fix this issue, this change moves the section to Cargo.toml of the root package.

Verifying this change

After this change is applied, we can confirm that opt-level is changed as expected.

$ cargo test -v --test demos --release
...
     Running `rustc --crate-name hello_wasm ... opt-level=s ...`
     Running `rustc --crate-name demos ... opt-level=s ...`

Documentation

No new docs as this PR introduces no new features.

[martin-g]

Do you have some reference to Cargo documentation explaining that this is the correct way ?
To me this looks like a bug in cargo that it ignores the package specific settings.

[sarutak]

This doc says like as follows.

Cargo only looks at the profile settings in the Cargo.toml manifest at the root of the workspace. Profile settings defined in dependencies will be ignored.

[martin-g]

Thank you, @sarutak !