fix: add normalizeFee, analyzeFeeHistory, and expose multi-op builders on client

[TheHalalHunter]

Summary

Resolves issues Sorokit#18, Sorokit#26, and Sorokit#62.

Changes

Issue Sorokit#26 - normalizeFee()

• Added normalizeFee(fee: string | number): string to src/shared/utils.ts
• Ensures fees are floored integer stroops before submission
• Exported from public API

Issue Sorokit#62 - analyzeFeeHistory()

• Created src/transaction/feeAnalytics.ts
• Computes min, max, avg, median, stddev, p25/p50/p75/p90/p95/p99
• Returns FeeHistoryAnalytics | null
• Exported from src/transaction/index.ts and src/index.ts

Issue Sorokit#18 - Multi-op builders on client

• Wired buildPaymentWithTrustline, buildSwapTransaction, buildReverseTransaction into SorokitClient.transaction
• Full error handling and logging consistent with existing methods
• PaymentWithTrustlineParams, SwapTransactionParams, ReverseTransactionParams exported from public API

Files Changed

• src/shared/utils.ts
• src/transaction/feeAnalytics.ts (new)
• src/transaction/index.ts
• src/client/createSorokitClient.ts
• src/index.ts