refactor(connector): added amount conversion to FISERV

## Type of Change
<!-- Put an `x` in the boxes that apply -->

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

## Description
<!-- Describe your changes in detail -->
added MinorUnit for amount conversion

### Additional Changes

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

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1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
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## Motivation and Context
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Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
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fixes #5947 

## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
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## Checklist
<!-- Put an `x` in the boxes that apply -->

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

<think>
PR Context:
- Title: refactor(connector): [FISERV, HELCIM] Add amount conversion framework to Fiserv, Helcim
- Merged: 2025-03-12T07:58:54Z
- Files changed: 8 files
- Commits: 13 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

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

## Description
<!-- Describe your changes in detail -->
added **FloatMajorUnit** for amount conversion for **Fiserv**
added **FloatMajorUnit** for amount conversion for **Helcim**

### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ 
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** refactor(connector): [FISERV, HELCIM] Add amount conversion framework to Fiserv, Helcim (#7336)
Co-a
Files to modify:


**crates/hyperswitch_connectors/src/connectors/fiserv.rs**
  Remove:
    - struct: pub::Fiserv
  Add:
    - function: pub::new
    - struct: pub::Fiserv

**crates/hyperswitch_connectors/src/connectors/fiserv/transformers.rs**
  Modify existing code

**crates/hyperswitch_connectors/src/connectors/helcim.rs**
  Remove:
    - struct: pub::Helcim
  Add:
    - function: pub::new
    - struct: pub::Helcim
    - impl: impl Helcim

**crates/hyperswitch_connectors/src/connectors/helcim/transformers.rs**
  Modify existing code

**crates/hyperswitch_connectors/src/utils.rs**
  Remove:
    - function: pub::str_to_f32

**crates/router/src/types/api.rs**
  Modify existing code

**crates/router/tests/connectors/fiserv.rs**
  Modify existing code

**crates/router/tests/connectors/helcim.rs**
  Modify existing code