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

首先檢視 PR #93 以及 ClassDef 和 FunctionDef 的 AST 定義，重點關注新增的 type_params 欄位和討論中描述的陳述式大小斷言。比較目前 Vec 與提議的 Box 方案對配置的影響，同時考慮提到的 tinyvec 替代方案；當所選表示能夠減少不必要的陳述式大小且不破壞 AST 時，工作就完成了。