feat(payment): PAYPAL-6495 add BCP venmo wallet strategy

[bc-yaroslav-zhmutskyi]

What/Why?

Add BigCommerce Payments Venmo Wallet strategy

Rollout/Rollback

Revert

Testing

Currently have issue with venmo login, will add recording after it resolved

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Note

Medium Risk
New payment wallet path touches order intent creation and tokenization proxying via PayPal SDK; pattern matches existing BCP wallet strategies but expands live Venmo cart checkout surface.

Overview
Adds a wallet button integration for BigCommerce Payments Venmo so merchants can show a Venmo wallet button on cart (or similar) surfaces, alongside the existing Venmo checkout button, customer, and payment strategies.

The new BigCommercePaymentsVenmoWalletStrategy validates methodId, containerId, and bigcommerce_paymentsvenmo options, decodes initializationData, loads the PayPal SDK, and renders PayPal Buttons with FUNDING.VENMO. On click it creates a payment order intent for provider bigcommerce_payments.venmo, and on approve it proxies tokenization for method bigcommerce_payments_venmo. Cart button styles from initialization data are normalized (including stripping gold color for Venmo), and the container is removed when the button is not eligible.

Registration wires the factory through PaypalCommerceWalletService with intent data key BigcommercePaymentWalletIntentData, resolved for method id bigcommerce_paymentsvenmo, and exports are added in the package index. Unit tests cover validation, SDK load, button rendering, order intent, approve flow, ineligibility, and factory instantiation.

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