Fix all clippy warnings and rustfmt across workspace

[colinrozzi]

Summary

• Resolve all 26 clippy lint errors (with -D warnings) across the workspace
• Apply cargo fmt to fix formatting inconsistencies (byte array layouts, chain expressions, etc.)
• All three CI checks now pass: cargo check, cargo clippy, cargo test

Key fixes

• #[derive(Default)] for Encoder instead of manual impl
• Collapse nested matches and else { if } blocks
• Replace redundant closures with function references
• Remove dead decode_type function
• Fix clone() on Copy types
• push_str("\n") → push('\n')
• Use char array patterns instead of chained || comparisons
• #[allow(clippy::too_many_arguments)] for cross_package_call

Test plan

• cargo clippy --workspace -- -D warnings passes
• cargo fmt --all -- --check passes
• cargo test --workspace — all 177 tests passing

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