[FEATURE] implement getFiatExchangeRate on WalletServices

[ac4ch]

Description of Changes

Provide a brief description of the changes you've made.

Linked Issues / Tickets

Reference any related issues or tickets, e.g. "Closes #123".

Testing Procedure

Describe the tests you've added or any testing steps you've taken.

• I have added new unit tests
• All tests pass locally
• I have tested manually in my local environment

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have run the linter

[github-actions]

Manual Tests

ℹ️ Remember to ask team members to perform manual tests and to assign tested label after testing.

[github-actions]

Manual Tests

💚 Manual testing by @cain4chain resulted in success.

[Copilot]

Pull Request Overview

This PR implements the getFiatExchangeRate method on WalletServices to support fiat currency exchange rate conversion functionality. The implementation allows users to convert between different fiat currencies using configurable exchange rates.

Key changes:

• Replaced panic placeholder with actual implementation of FiatExchangeRate method
• Added comprehensive unit tests covering various conversion scenarios and edge cases
• Created documentation and example code demonstrating the new functionality

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pkg/services/services.go	Implements the FiatExchangeRate method with currency conversion logic
pkg/services/services_fiat_exchange_test.go	Adds comprehensive test coverage for the new method
examples/services_examples/fiat_exhange_rate/fiat_exchange_rate.go	Provides example implementation demonstrating usage
examples/services_examples/fiat_exhange_rate/fiat_exchange_rate.md	Documentation explaining the feature and usage
examples/services_examples/nlock_time_is_final/nlock_time_is_final.go	Removes inline documentation comment
examples/services_examples/nlock_time_is_final/nlock_time_is_final.md	Adds separate documentation file

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud