feat: shared middleware function to build payment requirements

[0xf333]

Description

let’s have a single builder to construct PaymentRequirements, as mentioned in commit 26f132bf. besides, this will simplify maintenance and prevent implementation drifts

Tests

cd typescript && \
pnpm build && \
pnpm lint:check && \
pnpm --filter x402 exec vitest run src/shared/middleware.test.ts --reporter=verbose

Checklist

• [x] formatted and linted code
• [x] all new and existing tests pass
• [x] signed commits

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel[bot]]

@0xf333 is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.