fix: Resolve undefined symbol link errors in native tests using sol_interface

[Akagi201]

Description

closes issue #301

native (non-wasm) tests no longer hit undefined symbol link errors when using sol_interface!-generated interfaces. The added non-wasm hostio stubs supply the missing symbols, and the mock layer (mock_static_call / mock_call / mock_delegate_call) lets interface calls be tested. The new test sol_interface_mock_native.rs passes, proving the path works end to end.

tested with

cargo test -p stylus-sdk --features hostio --tests
cargo test -p stylus-sdk --features hostio sol_interface_static_call_mock
cargo test -p stylus-sdk --no-default-features --features storage-cache

Checklist

• I have documented these changes where necessary.
• I have read the DCO and ensured that these changes comply.
• I assign this work under its open source licensing.