Add requireBalance Capability for Spend Permissions

[spencerstock]

Summary

Keys now supports this - ready to merge into SDk

Added requireBalance capability support for spend permissions in both subscribe() and requestSpendPermission() functions. This capability enables wallets to verify that users have sufficient balance before creating a spend permission, preventing failed transactions due to insufficient funds.

Changes:

• Added requireBalance optional parameter to SubscriptionOptions type (defaults to true)
• Added WalletSignCapabilities type with requireBalance option for requestSpendPermission()
• Updated subscribe() to include capabilities in wallet_sign call when requireBalance is set
• Updated requestSpendPermission() to use wallet_sign (instead of eth_signTypedData_v4) when capabilities are provided
• Added validation and error handling for wallet_sign responses

How did you test your changes?

Added test coverage for:

• subscribe() with requireBalance: true - verifies capabilities are included in wallet_sign call
• subscribe() with requireBalance: false - verifies capabilities are excluded
• subscribe() with requireBalance: undefined - verifies default behavior (capabilities included)
• requestSpendPermission() with capabilities - verifies wallet_sign is used with proper parameters
• requestSpendPermission() without capabilities - verifies fallback to eth_signTypedData_v4
• Error handling for invalid wallet_sign responses

All tests pass. CI checks (lint, format, test, typecheck) pass.

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 2/1	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

[stephancill]

wallet_sendCalls' spend permission capability is called spendPermissions, would be nice to maintain consistency across them...