Use exact decimal arithmetic for payments, fees, quotes, and limits

[nwosum113-ui]

Summary

Implement exact decimal arithmetic for financial calculations to ensure precision and avoid floating-point errors in payments.

Changes

• Replaced floating-point arithmetic with exact decimal operations in payment-related services and utilities
• Updated validation logic to enforce decimal precision requirements
• Added unit tests to verify exact decimal behavior in financial calculations

Impact

• Payment Orchestrator: Ensures accurate payment calculations
• Compliance Service: Maintains precise financial compliance checks
• Pricing Service: Improves pricing accuracy
• Wallet Adapter: Enhances Stellar transaction precision
• Money Utilities: Centralizes exact decimal arithmetic logic
• Test Coverage: Validates financial calculations with exact decimals

closes #154

[vercel]

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2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
send-am-admin	Skipped		Aug 20, 2026 9:42am
senda	Skipped		Aug 20, 2026 9:42am

[Gozirimdev]

The decimal work is moving in the right direction, but we still need:

• Preserve exchange rates as decimals before JSON parsing can turn them into JavaScript numbers.
• Keep compliance totals separated by asset/currency and apply limits in a clearly defined currency.
• Support configured fiat currencies instead of a hard-coded list.
• Add a safe audit/reconciliation step for existing values.
• Add tests for mixed assets, rounding boundaries, large values, API output, and reconciliation.

Please finish these items before we merge.

[Gozirimdev]

This PR now conflicts with main and duplicates the decimal implementation already merged in #172. Please close this duplicate PR.