fix: Handle number inputs correctly in computeRoundingModulus

[matthewjablack]

Summary

This PR fixes a bug in the computeRoundingModulus function where number inputs were incorrectly treated as raw satoshi values instead of bitcoin amounts.

Problem

The computeRoundingModulus function accepts three types of inputs:

• Value objects (which have a .sats property)
• BigInt values (raw satoshi amounts)
• number values (intended to represent bitcoin amounts)

However, the function was treating number inputs as raw satoshi values, which caused incorrect calculations when users passed bitcoin amounts like 0.001 or 1.5.

Solution

• Number inputs: Now properly converted to satoshis by multiplying by 1e8 and rounding
• Value objects: Unchanged behavior (uses .sats property)
• BigInt inputs: Unchanged behavior (used directly as satoshi values)

Changes Made

• Updated computeRoundingModulus to use proper type checking and conversion
• Added comprehensive test coverage for all input types:
  • Bitcoin amount inputs (new functionality)
  • Value object inputs
  • BigInt inputs (raw satoshi values)
  • Mixed input scenarios
  • Edge cases (zero values, very small amounts)
• Updated existing tests to use BigInt for raw satoshi values

Backward Compatibility

• Breaking: Number inputs now represent bitcoin amounts instead of satoshi values
• Non-breaking: Value objects and BigInt inputs work exactly as before
• Existing code using Value objects or BigInt values is unaffected

Example Usage

// Before (incorrect): number treated as satoshis
computeRoundingModulus(100000, 100000000); // 100k sats, 100M sats

// After (correct): number treated as bitcoin amounts
computeRoundingModulus(0.001, 1.0);       // 0.001 BTC, 1.0 BTC
computeRoundingModulus(BigInt(100000), BigInt(100000000)); // For raw satoshi values

This fix ensures that the function behaves intuitively when working with bitcoin amounts while maintaining full compatibility with existing code that uses proper types.