refactor(router): add amount conversion framework to nexinets

[hex1c]

Type of Change

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

Description

Minor refactoring to standardizeNexinets connector to use the conversion framework to reduce potential inconsistencies in managing amounts fixes #6095 .

Additional Changes

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

Checklist

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

[semanticdiff-com[bot]]

Review changes with  

Changed Files

File	Status
crates/router/src/types/api.rs	85% smaller
crates/router/tests/connectors/nexinets.rs	69% smaller
crates/hyperswitch_connectors/src/connectors/nexinets/transformers.rs	38% smaller
crates/hyperswitch_connectors/src/connectors/nexinets.rs	30% smaller

[hex1c]

@awasthi21 review changes done

[deepanshu-iiitu]

@hex1c Please resolve the conflicts

[gorakhnathy7]

Hey @hex1c Can you please look into the comments, and make the changes!