feat(batch): add dryRun simulation option to submitBatch (closes #608)

[Ranjeet2063]

Summary

Adds a { dryRun: true } option to submitBatch that simulates every transaction against the Soroban RPC instead of broadcasting on-chain, returning would-be outcomes for pre-flight validation UIs without consuming sequence numbers or funds (closes #608).

Key Changes

• src/batch-tx.ts:
  • Added dryRun?: boolean to BatchSubmitOptions.
  • In submitBatch, when options.dryRun is enabled, simulates each transaction using server.simulateTransaction(tx).
  • Records SUCCESS for valid simulations and FAILED for simulation errors without calling server.sendTransaction or polling.
  • Enforces fail-fast behavior: marks subsequent transactions as SKIPPED upon the first simulation error.
• src/tests/batch-submit.test.ts:
  • Added unit test suite covering successful dry-run batches, simulation error handling with subsequent skips, and network/RPC simulation failures.

Verification

• vitest run src/tests/batch-submit.test.ts: 22/22 tests passing.
• Clean production build with npm run build.

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