ci: add GitHub Actions CI workflow

[jackhamer09-ai]

Summary

• Adds .github/workflows/ci.yml that runs on every PR and push to main
• Fixes all pre-existing clippy warnings so the baseline is clean from day one

What the CI checks

Step	Command	Purpose
Format	cargo fmt --check	Enforces consistent code style
Lint	cargo clippy -- -D warnings	Catches bugs and style issues; warnings are errors
Build	cargo build	Ensures the project compiles
Test	cargo test	Runs the test suite

Results are cached by Cargo.lock hash so repeated runs are fast.

Clippy fixes included

To make cargo clippy -- -D warnings pass cleanly on main, the following pre-existing warnings were fixed:

• Boxed large enum variant (TokenSubcommand::Send)
• Replaced redundant closures with function references (Address::from_str)
• Replaced .clone() on Copy types (FixedBytes<32>, tx hashes) with deref
• Removed .to_string() in format! args
• Fixed print_literal in println! format strings
• Replaced .get(0) with .first()
• Replaced print!("...\n") with println!
• Removed needless borrows
• Added #[allow(clippy::too_many_arguments)] on async relay functions
• Fixed field_reassign_with_default in Config::load
• Removed useless u64 identity conversion
• Fixed &PathBuf → &Path parameter type
• Fixed if_same_then_else in doctor command

Test plan

• PR CI runs and all steps pass (green checkmark)
• A follow-up PR with a fmt or clippy violation should be blocked

🤖 Generated with Claude Code