Add SDK batch operations support

[big14way]

Support batching multiple contract calls into a single transaction.

Acceptance Criteria:

• Add BatchBuilder class
• Support adding multiple operations
• Build and return single transaction

Files: new file sdk/src/batch.ts, sdk/src/index.ts

[lustsazeus-lab]

Batch ops would be a big usability win. One guardrail worth adding early: make BatchBuilder enforce deterministic op ordering + explicit per-op failure handling semantics.

That keeps signed payloads predictable and avoids ambiguity when one op in the batch fails on-chain.

[lustsazeus-lab]

Completed Issue #6 (batch ops scaffold).

• Added src/batch.ts with BatchBuilder and support for multi-op assembly (order/mode).
• Exported via SoroSaveClient (createBatchBuilder, buildBatchTransaction).
• Added tests in tests/batch.test.ts.
• Commit: 6d015e2 in PR feat: wallet adapter abstraction and batch ops scaffolding #73 (feat: wallet adapter abstraction and batch ops scaffolding #73).
• Verified: npm run build, npm test.

[lustsazeus-lab]

Completed Issue #6 (batch ops scaffold).

• Added src/batch.ts with BatchBuilder and support for multi-op assembly (order/mode).
• Exported via SoroSaveClient (createBatchBuilder, buildBatchTransaction).
• Added tests in tests/batch.test.ts.
• Commit: 6d015e2 in PR feat: wallet adapter abstraction and batch ops scaffolding #73 (feat: wallet adapter abstraction and batch ops scaffolding #73).
• Verified: npm run build, npm test.