feat: add authorization_type and payment_plan to hosted, link and session payment requests

[armando-rodriguez-cko]

Summary

Adds two properties that swagger introduced to HostedPaymentsRequest, PaymentLinksRequest and CreatePaymentSessionsBaseRequest but were missing from the corresponding PHP request classes:

• authorization_type — string, allowed values Final / Estimated (default Final). Matches how PaymentRequest already exposes authorization_type as a plain string property. (Note: the existing Checkout\AuthorizationType class is for SDK auth modes, not payment authorization, so it is intentionally not reused.)
• payment_plan — typed as the existing Checkout\Payments\PaymentPlan, which already maps the PaymentSessionPaymentPlanRecurring schema. Added the one missing field amount_variability (Fixed/Variable) to that class.

Applied to:

• lib/Checkout/Payments/Hosted/HostedPaymentsSessionRequest.php
• lib/Checkout/Payments/Links/PaymentLinkRequest.php
• lib/Checkout/Payments/Sessions/PaymentSessionsRequest.php

Part of a cross-SDK sweep aligning request models with recent swagger additions.

Tests

Added test/Checkout/Tests/Payments/PaymentRequestFieldsSerializationTest.php covering serialization of both new fields across all three request classes, plus omission of unset fields.

vendor/bin/phpunit test/Checkout/Tests/Payments/PaymentRequestFieldsSerializationTest.php
OK (4 tests, 12 assertions)
vendor/bin/phpunit test/Checkout/Tests/JsonSerializerTest.php
OK (7 tests, 8 assertions)

PHP lint + phpcs pre-commit hook passed on all changed files.

Follow-up

None required for typing — PaymentPlan was a good fit and only needed amount_variability added.

[sonarqubecloud]

Quality Gate failed

Failed conditions
B Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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