refactor(routing): de-couple dynamic and static routing

[prajjwalkumar17]

Type of Change

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

Description

This pull request refactors the routing logic in the payments core to introduce a new extensible routing pipeline using the RoutingStage trait and associated stage structs. The changes modularize static and dynamic routing logic, encapsulate routing results, and simplify dynamic routing integration with Open Router. This makes the routing process more maintainable and extensible for future enhancements.

Routing Pipeline Refactor and Abstractions:

• Introduced a new RoutingStage async trait and implemented it for StaticRoutingStage and (conditionally) DynamicRoutingStage, allowing routing logic to be composed as a pipeline of stages. The apply method encapsulates each stage's logic and takes/returns a new RoutingOutcome struct.
• Added the RoutingOutcome struct to carry connectors and routing approach through the pipeline, replacing ad-hoc tuple passing.

Core Routing Logic Changes:

• Refactored the main routing function in payments.rs to use the new pipeline: first applying the static routing stage, then (if enabled) the dynamic routing stage, updating the payment data with the final routing approach.
• Updated connector data extraction to use the new RoutingOutcome struct.

Dynamic Routing Integration:

• Refactored dynamic routing with Open Router to return a new DynamicRoutingResult struct, encapsulating connectors and routing approach, and updated all call sites to use this new result type. [1] [2] [3] [4] [5] [6] [7]

Dependency and Import Updates:

• Added necessary imports for the new trait and struct usage, such as RoutingStage.

Additional Changes

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

Motivation and Context

How did you test it?

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]

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Changed Files

File	Status
crates/router/src/core/payments.rs	16% smaller
crates/router/src/core/payments/routing.rs	6% smaller
crates/router/src/core/routing.rs	0% smaller

[codecov]

Codecov Report

❌ Patch coverage is 21.21212% with 26 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@46bb969). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
crates/router/src/core/payments/routing.rs	0.00%	26 Missing ⚠️

Additional details and impacted files

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