fix: add simple codiff class

[zhanba]

fix #1

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	31.19%	2450 / 7853
🔵	Statements	31.19%	2450 / 7853
🔵	Functions	26.75%	126 / 471
🔵	Branches	79.31%	372 / 469

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
packages/codiff/src/codiff.ts	63.36%	66.66%	83.33%	63.36%	49-50, 55-61, 81-107, 112-113
packages/codiff/src/index.ts	0%	0%	0%	0%	1-3
packages/codiff/src/common/cache.ts	53.12%	42.85%	60%	53.12%	18-21, 30-31, 38-42, 46-47, 53-54
packages/codiff/src/diff/index.ts	0%	0%	0%	0%	1-6
packages/playground/src/App.tsx	0%	0%	0%	0%	1-203

Generated in workflow #4 for commit de1b1c0 by the Vitest Coverage Report Action