Stop collecting a Google Pay billing address by default (breaking)

[Max Harrison (maxharrison)]

Stacked on #70. Review that first.

Breaking change. Do not merge before a major Android SDK release.

Config.billingAddress now defaults to BillingAddressConfig.Disabled instead of BillingAddressConfig.Enabled().

Merchants who relied on the implicit billing address request must now opt in:

Config(
    appId = appId,
    merchantId = merchantId,
    billingAddress = BillingAddressConfig.Enabled(),
)

Why

Collecting a billing address that the integrator never asked for is the wrong default for a payments SDK. The web SDK has always treated it as opt-in, so Android is the outlier.

Risk

A merchant who uses the billing address for AVS or for fraud rules loses that data on upgrade, with no error and no compile failure. That can move authorisation rates. A release note is the only signal, which is why this waits for a major version rather than riding a minor.

What changes

• Config.billingAddress default.
• PaymentRequestTest splits the old default assertion into a default case and an explicitly enabled case.
• GooglePayGoldenRequestTest points the default case at the billing-disabled fixture. That one-line diff is the whole behaviour change, which is the point of landing the goldens first.

[Max Harrison (maxharrison)]

Reopened as #72 after the stack was reordered. GitHub auto-closed this one as merged into its former stack base; nothing landed on main.