Add unit tests to ensure submodules are causal and streamable

[jerryli27]

Checklist

• [ X ] Read CONTRIBUTING.md, and accept the CLA by including the provided snippet. We will not accept PR without this.
• [ X ] Run pre-commit hook.
• [ X ] If you changed Rust code, run cargo check, cargo clippy, cargo test.

PR Description

Add unit tests to check that the following submodules are causal and streamable:

• StreamingConv1d
• StreamingConvTranspose1d
• SEANetResnetBlock
• SEANetDecoder

Please see the related issue for more context.

CLA Snippet:

I, jerryli27, confirm that I have read and understood the terms of the CLA of Kyutai-labs, as outlined in the repository's CONTRIBUTING.md, and I agree to be bound by these terms.

[LaurentMazare]

Thanks!