Consider using `Box` on type parameters to reduce statement allocation size

In https://github.com/RustPython/Parser/pull/93, we add type_params: Vec to ClassDef and FunctionDef which increases the size of a statement. We may want to optimize this field to reduce the size of the statement struct.

The main reason for the assertion is to be aware of how changing the AST changes its size. This is important because ruff and RustPython hold many instances of these types and increasing their size mean:

• Each element in a Vec now requires more storage -> Overall increased memory consumption
• Reading or writing an element becomes slower because your computer must read or write more bytes. This is especially relevant for reading where the L1 cache short circuits reads by caching about 64 bytes of neighboring memory to avoid subsequent reads from (the very slow) memory.

There's not much we can do about this here. This could be a place where using tinyvec over a regular Vec would be beneficial, considering that the vec will be empty for almost all instances. But I think this is fine for now.

Originally posted by @MichaReiser in https://github.com/RustPython/Parser/pull/93#discussion_r1259220991

まず PR #93 と ClassDef および FunctionDef の AST 定義を確認し、追加された type_params フィールドと、議論で説明されている文のサイズに関するアサーションに注目してください。現在の Vec によるアロケーションへの影響と、提案されている Box アプローチを比較し、言及されている tinyvec の代替案も考慮してください。選択した表現によって不要な文のサイズが削減され、AST を壊さなければ作業は完了です。