Which issue does this PR close?

Closes #7152 .

Rationale for this change

This PR adds initial support for Volcengine TOS, a cloud object storage service provided by Volcengine (ByteDance).

What changes are included in this PR?

• This PR provides the basic service infrastructure. The backend currently has all capabilities disabled (read, write, delete, list, stat) as this is a foundation commit. Subsequent PRs will implement the actual storage operations.
• Added services-tos feature

Are there any user-facing changes?

Users can now configure and initialize a TOS service builder, though operations are not yet functional. Configuration can be done via:

use opendal::services::Tos;
let builder = Tos::default()
       .bucket("my-bucket")
       .endpoint("https://tos-cn-beijing.volces.com")
       .access_key_id("your-access-key-id")
       .secret_access_key("your-secret-access-key");
let op = Operator::new(builder)?.finish();

AI Usage Statement

AI assistance was used during development. The code has been thoroughly reviewed and tested by me, and I take full responsibility for it.