feat: align transparent checkout contracts

[lleonardo-franco]

Summary

• Align v2 transparent checkout contracts for PIX and BOLETO across types, Zod, and TypeBox
• Add SDK transparent checkout helpers for create, list, simulate, and status
• Keep pix.create compatibility while sending the documented { method, data } body shape
• Add focused tests and README examples for the updated contracts

Validation

• bun run typecheck
• bun run test
• bun run build
• bunx biome check on changed files

Closes #23