Reduce size of Stmt from 144 to 120 bytes

[carljm]

Summary

I happened to notice that we box TypeParams on StmtClassDef but not on StmtFunctionDef and wondered why, since StmtFunctionDef is bigger and sets the size of Stmt.

@charliermarsh found that at the time we started boxing type params on classes, classes were the largest statement type (see #6275), but that's no longer true.

So boxing type-params also on functions reduces the overall size of Stmt.

Test Plan

The <= size tests are a bit irritating (since their failure doesn't tell you the actual size), but I manually confirmed that the size is actually 120 now.

[codspeed-hq]

CodSpeed Performance Report

Merging #11051 will improve performances by 6.13%

_{Comparing box-type-params (74b2d51) with main (99f7f94)}

Summary

⚡ 1 improvements
✅ 29 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	box-type-params	Change
⚡	parser[unicode/pypinyin.py]	1.7 ms	1.6 ms	+6.13%

[charliermarsh]

Thanks!

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.