test: add comprehensive unit tests for usePathPayment - strict-send and strict-receive modes

[believetimothy]

Summary

Adds 13 new unit tests to usePathPayment.test.ts, expanding coverage from 8 to 21 tests. The new tests cover both strict-send and strict-receive modes with better asset resolution, Horizon/Stellar SDK interaction verification, and edge case handling.

Changes

New Strict-Send Tests

• Credit send asset resolution — verifies new Asset(code, issuer) is called for credit-type send assets
• Native destination asset — verifies Asset.native() is called for native-type dest assets
• Default empty path — confirms an empty array is passed when no path option is provided
• Horizon Server creation — validates server is created with config.horizonUrl
• TransactionBuilder params — checks fee and networkPassphrase are forwarded correctly
• Custom timeoutSeconds — ensures custom timeout flows through
• Source account loading — verifies loadAccount is called with the correct publicKey
• Builder chaining — confirms addOperation and setTimeout are invoked on the TransactionBuilder
• reset() delegation — verifies reset delegates to useTransaction
• Null publicKey error — properly tests the hook throws when Freighter is disconnected (using mutable mock via vi.hoisted)
• Credit send to native dest parameter mapping — validates sendAmount and destMin with mixed asset types

New Strict-Receive Tests

• sendMax / destAmount mapping — confirms sendAmount maps to sendMax and destMin maps to destAmount
• Credit to credit path — validates parameter mapping for credit send and credit dest
• Native to native path — validates parameter mapping with both assets as native

Infrastructure

• Used vi.hoisted to create a mutable publicKey mock, avoiding hoisting issues with inline vi.mock calls inside test bodies

Test Plan

 ✓ src/__tests__/usePathPayment.test.ts  (21 tests)
Test Files  1 passed (1)
Tests  21 passed (21)

Closes dark-princezz#141