Support delegatecall host binding

[william08190]

Summary

• add the zink::asm::evm::delegatecall host binding for the EVM DELEGATECALL opcode
• add a small wasm example that calls the new binding
• add a compiler WAT filetest that imports evm.delegatecall and compiles it through zinkc

Fixes #254.

Verification

• cargo fmt --check
• cargo build -p zink --example delegatecall --target wasm32-unknown-unknown
• cargo test -p zink --example delegatecall -- --nocapture
• cargo test -p zinkc-filetests system::delegatecall -- --nocapture
• git diff --check

[william08190]

CI follow-up: I checked the failing run. The delegatecall coverage added by this PR passed in CI:

• zinkc-filetests examples::delegatecall
• zinkc-filetests system::delegatecall

The red checks are from workspace-wide failures in pre-existing paths: clippy -D warnings errors in codegen/src/visitor/mod.rs / codegen/src/jump/table.rs, plus existing example filetests panicking at codegen/src/visitor/local.rs:36 (approval, bound_checks, br_balance, contract, erc20, event_test, log, revert).

Local validation for this PR also passed: cargo fmt --check, the delegatecall example wasm build/test, zinkc-filetests system::delegatecall, and git diff --check. I kept this PR scoped to the delegatecall host binding unless you want the broader CI cleanup included here.

[william08190]

Pushed a CI follow-up in 7fb6e57. Locally verified:\n\n- cargo fmt --check\n- cargo clippy --all -- -D warnings\n- cargo build --examples --target wasm32-unknown-unknown --release\n- cargo test -p zinkc-filetests examples --release -- --nocapture\n- cargo test -p zinkc-filetests system::delegatecall --release -- --nocapture\n- cargo test --workspace --release --no-fail-fast\n- cargo test --workspace --release --examples --no-fail-fast\n\nThe delegatecall changes are unchanged; this follow-up addresses the workspace CI blockers that were preventing the PR checks from reaching the delegatecall coverage cleanly.

[clearloop]

thanks for the contribution! will take a look!