feat: wallet adapter abstraction and batch ops scaffolding

[lustsazeus-lab]

Summary

• Adds wallet adapter abstraction and Freighter adapter for SDK signing paths (Issue Add SDK wallet adapter abstraction #10).
• Adds BatchBuilder utility and client helpers for batched operation transactions (Issue Add SDK batch operations support #6).
• Adds integration test scaffold with Soroban placeholder path (Issue Create SDK integration test suite #9).
• Includes unit tests for deterministic batch ordering and failure-mode summary.

Validation

• npm run build
• npm test

Notes

This branch includes non-breaking additions to SDK API surface; integration test for #9 is added as a skip with explicit TODO steps for local Soroban container setup.

[lustsazeus-lab]

Update (issue #9 integration):

这次同步把原先占位测试补齐为可执行内容。

PR 更新

• Commit: 0fa9691
• 变更文件：tests/integration.test.ts
• 变更内容：
  • 将 it.skip 占位替换为完整可执行的 mock lifecycle 测试
  • 覆盖 wallet adapter + 生命周期调用 + batch 构建断言 + read-model 解析断言
  • 增加 local Soroban 节点可选分支（skipIf）

验证

• npm test -- tests/integration.test.ts

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[lustsazeus-lab]

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