Assemble full release

[midenotch]

Closes #80

---

Close: #80

Implemented releaseFunds() in [src/escrow/index.ts] and re-exported it from [src/index.ts]

It now:

converts the balance to stroops and uses BigInt arithmetic for percentage math
builds one Payment operation per distribution entry
preserves exact 7-decimal formatting
distributes any leftover stroops by remainder so the split always sums back to the original balance
I also added unit coverage in [tests/unit/escrow/index.test.ts]
for:

500 XLM with 60/40 => 300.0000000 and 200.0000000
100% to a single recipient
a three-way split that sums exactly to the starting balance
Verification: npm test -- --runInBand passed with 81/81 tests green.

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[amina69]

@midenotch , test failed