docs(prepareSpendCallData): replace Promise.all with sequential awaits in eth_sendTransaction example

[Sertug17]

The eth_sendTransaction example in the prepareSpendCallData JSDoc used Promise.all to submit the calls, but the comment claimed they would execute "in exact order":

// Or send the calls using eth_sendTransaction to submit both calls in exact order
const promises = spendCalls.map((call) => provider.request({ ... }))
await Promise.all(promises);

Promise.all submits all requests concurrently there is no guarantee that approveWithSignature confirms before spend is mined. For a not-yet-approved permission, both transactions can land in the same block, causing spend to revert because the permission isn't approved yet.

This PR replaces the example with a sequential for...of loop that awaits each call before submitting the next, and adds a comment explaining why Promise.all is unsafe here and why wallet_sendCalls with atomicRequired: true is the recommended path.

No code changes JSDoc comment only.

[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