codegen fails to compile with indexmap 2.x in no_std + alloc mode

codegen fails to compile when indexmap is used without default features (i.e. no_std + alloc mode). In this configuration, IndexMap requires an explicit hasher type parameter and no longer provides IndexMap::new(). The current codegen source assumes std is always available, which breaks in no_std contexts.

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Steps to Reproduce

1. Update Cargo.toml dependency:

   [dependencies] indexmap = { version = "2.11", default-features = false }

2. Build with nightly Rust:

   cargo +nightly build

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Observed Behavior

Compilation fails with errors such as:

error[E0107]: struct takes 3 generic arguments but 2 generic arguments were supplied error[E0599]: no function or associated item named `new` found for struct `IndexMap<K, V, S>`

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Expected Behavior

codegen should compile successfully with indexmap in no_std + alloc mode by:

• Providing explicit RandomState or generic hasher arguments.
• Replacing IndexMap::new() with IndexMap::with_hasher(...).