feat: Implement UCS granular flows with gateway context refactoring

[hrithikesh026]

Based on the git diff analysis, I can see this is a significant refactoring PR that implements UCS (Unified Connector Service) granular flows. Let me create a comprehensive PR description and title for you.

PR Title

feat: Implement UCS granular flows with gateway context refactoring

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

This PR implements a major refactoring to support granular flows in the Unified Connector Service (UCS) architecture. The changes include:

Core Changes:

1. Gateway Context Refactoring: Introduced RouterGatewayContext as a unified context structure passed throughout payment flows
2. UCS Granular Flows Support: Extended granular gateway support to Authorize and SetupMandate flows (previously only PSync)
3. Dependency Updates: Updated connector-service dependency from rev b5a367c1 to 452d4966
4. Flow Interface Updates: Modified all payment flow traits to accept gateway context parameter

Key Technical Changes:

• Added gateway_context parameter to all flow methods (add_access_token, add_session_token, add_payment_method_token, etc.)
• Refactored UCS response handlers to return simplified response types
• Updated transformer implementations for better address handling
• Enhanced gateway context creation with default constructor
• Improved error handling and response mapping in UCS integration

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

This change is required to enable granular flow support in the Unified Connector Service architecture. The previous implementation had limited UCS support and inconsistent context handling across different payment flows. This refactoring:

1. Standardizes Context Management: Provides a unified way to pass gateway context through all payment flows
2. Enables Granular UCS Support: Extends UCS capabilities to Authorize and SetupMandate flows
3. Improves Maintainability: Reduces code duplication and provides consistent interfaces
4. Enhances Debugging: Better context tracking for payment flow execution

How did you test it?

The changes should be tested with:

1. Unit Tests: Test the new gateway context creation and default constructor
2. Integration Tests: Verify Authorize and SetupMandate flows work with UCS
3. Manual Testing: Test payment flows with connectors that support granular UCS operations
4. Regression Testing: Ensure existing PSync and direct connector flows continue to work

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
crates/router/src/core/payments/access_token.rs	94% smaller
crates/router/src/core/unified_connector_service/transformers.rs	67% smaller
crates/router/src/core/payments/gateway.rs	65% smaller
crates/router/src/core/payments/flows/setup_mandate_flow.rs	60% smaller
crates/router/src/core/payments/flows/authorize_flow.rs	56% smaller
crates/router/src/core/payments/flows/session_flow.rs	49% smaller
crates/router/src/core/payments/flows/complete_authorize_flow.rs	49% smaller
crates/router/src/core/unified_connector_service.rs	47% smaller
crates/router/src/core/payments/gateway/setup_mandate.rs	25% smaller
crates/router/src/core/refunds.rs	22% smaller
crates/router/src/core/payments/flows/external_proxy_flow.rs	20% smaller
crates/router/src/core/payments.rs	16% smaller
crates/router/src/core/payments/customers.rs	11% smaller
crates/router/src/core/payments/tokenization.rs	8% smaller
crates/router/src/core/payments/helpers.rs	2% smaller
crates/router/src/core/payments/gateway/context.rs	2% smaller
Cargo.lock	Unsupported file format
crates/external_services/Cargo.toml	Unsupported file format
crates/hyperswitch_domain_models/src/router_flow_types/access_token_auth.rs	0% smaller
crates/hyperswitch_domain_models/src/router_request_types.rs	0% smaller
crates/hyperswitch_interfaces/Cargo.toml	Unsupported file format
crates/router/Cargo.toml	Unsupported file format
crates/router/src/core/payments/flows.rs	0% smaller
crates/router/src/core/payments/flows/approve_flow.rs	0% smaller
crates/router/src/core/payments/flows/cancel_flow.rs	0% smaller
crates/router/src/core/payments/flows/cancel_post_capture_flow.rs	0% smaller
crates/router/src/core/payments/flows/capture_flow.rs	0% smaller
crates/router/src/core/payments/flows/extend_authorization_flow.rs	0% smaller
crates/router/src/core/payments/flows/incremental_authorization_flow.rs	0% smaller
crates/router/src/core/payments/flows/post_session_tokens_flow.rs	0% smaller
crates/router/src/core/payments/flows/psync_flow.rs	0% smaller
crates/router/src/core/payments/flows/reject_flow.rs	0% smaller
crates/router/src/core/payments/flows/session_update_flow.rs	0% smaller
crates/router/src/core/payments/flows/update_metadata_flow.rs	0% smaller
crates/router/src/core/payments/gateway/access_token_gateway.rs	0% smaller
crates/router/src/core/payments/gateway/authorize_gateway.rs	0% smaller
crates/router/src/core/payments/gateway/create_order_gateway.rs	0% smaller
crates/router/src/core/payments/gateway/payment_method_token_create_gateway.rs	0% smaller
crates/router/src/core/payments/gateway/session_token_gateway.rs	0% smaller
crates/router/src/core/payments/vault_session.rs	Unsupported file format
crates/router/src/core/refunds_v2.rs	Unsupported file format

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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  Coverage        ?    9.14%           
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  Files           ?      186           
  Lines           ?    19386           
  Branches        ?        0           
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  Hits            ?     1773           
  Misses          ?    17613           
  Partials        ?        0           

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