feat: implement auto-retry mechanism for RPC calls (fixes #36)

[AlAfiz]

feat: retry RPC calls (#36)

Description: Adds executeRpcWithRetry to handle flaky Stellar Horizon connections.

Retries: 10 attempts, exponential backoff.
Log: Warns on 3rd failure.
Abort: Stops on 4xx errors (except 429).
Fixes: #36

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Issue	Title
#73	#38 Issue 38: [Config] Multi-Network Environment Support	Link to this issue
#74	#39 Issue 39: [Analytics] Admin "Top Claimers" Dashboard API	Link to this issue
#71	#36 Issue 36: [Ops] Auto-Retry Mechanism for RPC Calls	Link to this issue
#72	#37 Issue 37: [Database] Cold Storage for Completed Vaults	Link to this issue

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