Split seafile out of core

[Sahil-Shadwal]

Which issue does this PR close?

Closes #6920
Tracking issue: #6829

Rationale for this change

This PR splits the seafile service out of core into its own crate opendal-service-seafile as part of the core-split effort (RFC-6828). This modularizes the codebase and allows for better dependency management.

What changes are included in this PR?

• Moved seafile service code from core/src/services/seafile to new crate at core/services/seafile.
• Created core/services/seafile/Cargo.toml with necessary dependencies.
• Updated core/Cargo.toml to add opendal-service-seafile to the workspace and dependencies.
• Updated core/src/lib.rs to re-export the seafile service.
• Updated opendal-core to remove the old seafile module and feature flags.

Are there any user-facing changes?

No. The public API and behavior remain unchanged as the service is re-exported from the wrapper crate.

AI Usage Statement

Tools: Copilot , gemini 3

[Xuanwo]

Hi, please fill the AI Usage Statement

[Sahil-Shadwal]

@Xuanwo the reason for fail of OpamSolution.Fetch_fail in BInding OCaml is hash mismatch

- name: Checks
         run: |
           opam update.  # added line
           opam install -y dune ounit2 ocamlformat
           eval $(opam env)
           cd bindings/ocaml

should i create a issue and add this to yml or just add it here?