refactor(connector): Migrate Zsl connector from get_amount_as_string to new AmountConvertor

[nabeel001]

Type of Change

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

Description

refactor(connector): implement amount conversion framework for Zsl

• Replace outdated get_amount_as_string with new AmountConvertor framework
• Add StringMinorUnitForConnector to Zsl struct for centralized amount conversion
• Update ZslRouterData to use StringMinorUnit instead of String for type safety
• Update connector mappings and feature matrix to use new constructor
• Maintain backward compatibility with existing API structure

closes #9096

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]

Review changes with  

Changed Files

File	Status
crates/router/src/types/api/connector_mapping.rs	79% smaller
crates/router/src/types/api/feature_matrix.rs	79% smaller
crates/router/tests/connectors/zsl.rs	45% smaller
crates/hyperswitch_connectors/src/connectors/zsl/transformers.rs	45% smaller
crates/hyperswitch_connectors/src/connectors/zsl.rs	10% smaller

[Anurag-05-prog]

Hi @nabeel001,
Please run cargo run command and resolve warnings and errors if any.