fix: resolve compilation and formatting errors on main

[marcmantei]

Fixes clippy lint errors that were preventing CI from passing on the main branch.

Changes

• Collapsed nested if statement into match guard in opencode_stream.rs test
• All cargo clippy checks now pass with zero errors
• All cargo fmt checks now pass

Verification

• ✅ cargo check --all-targets --all-features
• ✅ cargo clippy --all-targets --all-features
• ✅ cargo fmt --all --check