Replace derive_more event helpers with a local macro

[joshka]

Summary

This removes the derive_more dependency and feature used to provide the event enum is_* methods.

The public methods and their behavior remain unchanged. They are now generated by a small private macro_rules! macro, while payload-sensitive predicates remain handwritten.

This follows the direction discussed in PR #949, where the tradeoff between boilerplate and an additional proc-macro dependency was discussed. PR #970 subsequently made the dependency optional, but it was still enabled by default.

Why

The generated methods are all simple variant checks, so requiring downstream users to compile derive_more and its proc-macro dependencies is disproportionate to the behavior being added.

The local macro keeps the declarations concise and consistent:

impl_is_variant! {
    Event {
        FocusGained => is_focus_gained,
        Key(..) => is_key,
        Mouse(..) => is_mouse,
    }
}

The variants previously marked is_variant(ignore)—KeyCode::F, Char, Media, and Modifier—are intentionally omitted from the macro. They already have handwritten payload-aware methods: is_function_key, is_char, is_media_key, and is_modifier. This avoids duplicate or conflicting methods while preserving their value-sensitive behavior.

Compile-time comparison

These were clean, isolated builds on the same machine and toolchain:

Benchmark	Local macro	derive_more	Difference
Clean crossterm cargo build	2.41s	3.41s	+1.00s
Fresh consumer cargo check	2.12s	3.00s	+0.88s

The derive_more build additionally compiled proc-macro dependencies including syn, quote, convert_case, derive_more-impl, and derive_more.

For context, PR #949 measured the original fresh-project comparison at 1.851s versus 3.539s, and a clean M2 crate build at 2.016s versus 2.688s. Exact timings vary by toolchain and machine, but the direction is consistent.

Validation

• cargo fmt --check
• cargo test --all-targets --locked
• cargo test --no-default-features --all-targets --locked
• cargo test --all-features --all-targets --locked
• cargo clippy --all-targets --all-features --locked -- -D warnings
• cargo doc --no-deps --all-features --locked

cc @archseer @the-mikedavis