Support f32/f64 float literals in paste! macro

[Copilot]

The paste! macro failed on float literals with type suffixes ([< 0.0 f32 >] → "unsupported literal") and on negative float literals ([< -0.0 f32 >] → "unexpected punct"), making it impossible to concatenate float values and type suffixes.

Changes

• src/segment.rs — Accept - punctuation as a valid segment (value "-"), enabling negative numeric literal construction.

• src/lib.rs — parse_bracket_as_segments

  • Introduce is_numeric_literal guard: digit-starting strings without + (e.g. 0.0, 1.5f32) bypass the ./+/\ rejection check. 1e+100 and byte literals still fail as before.
  • Restrict replace('-', "_") to quoted string/char literal content only — prevents the - punct segment from being silently mangled to _.

• src/lib.rs — pasted_to_tokens — Handle pasted strings starting with - followed by a digit by emitting a - Punct token + the parsed numeric literal, matching how Rust represents negated literals.

Example

paste! {
    let _ = [< 0.0 f32 >];    // 0.0f32 ✓
    let _ = [< -0.0 f32 >];   // -0.0f32 ✓
    let _ = [< 1.0 f64 >];    // 1.0f64 ✓
}