Add getFeeStats method and fees endpoint with Redis caching

[Adedayo-Data]

Description

Adds a new endpoint GET /chain/fees to retrieve the current base fee and resource fee estimates from the configured Soroban RPC.

Changes

• Implemented getFeeStats() in StellarService to fetch inclusion fee statistics from Soroban RPC and read the base fee from the latest closed ledger.
• Added GET /chain/fees endpoint to ChainController.
• Integrated Redis caching on the endpoint with a 30-second TTL (chain:fees) to prevent hammering the Soroban RPC.
• Fixed a pre-existing duplicate model definition in the Prisma schema to allow compilation.
• Fixed a pre-existing path import depth issue in address-param.dto.ts.
• Added unit tests in chain.controller.spec.ts and stellar.service.spec.ts to verify the fee retrieval and caching functionality.

closes #293

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