test: widen fee-payer server coverage

[brendanjryan]

Summary

• run the Tempo session server lifecycle and middleware adapter tests through both direct and fee-payer variants
• add Elysia session coverage and broaden the shared test signing helpers so sponsored open/topUp transactions can be generated in tests
• keep the existing close-path assertions under direct mode where the current localnet fee-payer close path is not exercised end-to-end

Testing

• pnpm check
• pnpm check:types
• pnpm test -- src/tempo/server/Session.test.ts src/middlewares/express.test.ts src/middlewares/hono.test.ts src/middlewares/nextjs.test.ts src/middlewares/elysia.test.ts

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/mppx@252

commit: c20b6c8