chore: release v4.0.0

[Boshen]

🤖 New release

• oxc_index: 3.1.0 -> 4.0.0 (⚠ API breaking changes)

⚠ oxc_index breaking changes

--- failure trait_associated_const_added: non-sealed trait added associated constant without default value ---

Description:
A non-sealed trait has gained an associated constant without a default value, which breaks downstream implementations of the trait
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-item-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.43.0/src/lints/trait_associated_const_added.ron

Failed in:
  trait constant oxc_index::Idx::MAX in file /tmp/.tmpgQzCch/oxc-index-vec/src/lib.rs:200

--- failure trait_method_added: pub trait method added ---

Description:
A non-sealed public trait added a new method without a default implementation, which breaks downstream implementations of the trait
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-new-item-no-default
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.43.0/src/lints/trait_method_added.ron

Failed in:
  trait method oxc_index::Idx::from_usize_unchecked in file /tmp/.tmpgQzCch/oxc-index-vec/src/lib.rs:206

Changelog

4.0.0 - 2025-09-30

Added

• add const support to methods where possible (#87)
• add NonMaxU32 support via define_nonmax_index_type! macro (#86)

Fixed

• reorder attributes in define_nonmax_index_type! for proc macro compatibility

Other

• cargo fmt
• make serde and nonmax optional features
• make nonmax support always available and use crate's own nonmax
• make serde support always available and use crate's own serde
• add documentation to all public methods to fix missing_docs warnings
• remove backward compatibility alias for define_nonmax_index_type!
• rename define_nonmax_index_type! to define_nonmax_u32_index_type!
• apply tuple struct pattern to define_index_type! macro
• remove #[repr(transparent)] from define_nonmax_index_type!
• change define_nonmax_index_type! to use tuple struct pattern
• document custom attribute support in define_nonmax_index_type!
• remove bounds check from IndexVec::push (#84)

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This PR was generated with release-plz.