feat: Stellar RPC client, health monitoring, and Vitest migration

[precious-akpan]

Summary

This PR implements a robust, type-safe Stellar RPC client with retry logic and configurable timeouts. It also synchronizes the branch with the latest upstream changes, including the transition to Vitest and the new Express factory pattern.

Closes #18
Relates to #41

Changes

• Stellar RPC Client: Added a type-safe wrapper for 'StellarSdk.rpc.Server' with exponential backoff and timeout handling.
• Health Monitoring: Integrated 'assessIndexerHealth' with '/health/live' and '/health/ready' endpoints.
• Infrastructure: Refactored 'app.ts' to follow the upstream factory pattern while incorporating correlation ID and request logging middleware.
• Test Suite: Migrated the entire codebase from 'node:test' to 'Vitest' to align with the new upstream testing standards.

Verification

• Ran full Vitest suite (290+ tests).
• Manually verified health endpoints and RPC retry logic.
• Verified Stellar transaction on-chain verification in stream creation flows.

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[Jagadeeshftw]

please resolve the conflicts @precious-akpan

[precious-akpan]

During the process of resolving merge conflicts for this PR, several regressions were identified in the current upstream/main branch:

Broken Application Initialization: src/app.ts in the base branch is missing critical initialization and export logic for the app instance, causing widespread test failures.
Strict Type Checking: Recent updates to tsconfig.json (specifically noUncheckedIndexedAccess) have introduced new compilation errors in existing test suites.
Empty Test Suites: Several new suites (e.g., src/webhooks/signature.test.ts) are currently empty, which causes Jest to fail.
Double jest config files.
I am proceeding with resolving these inherited issues alongside the merge conflicts to ensure this PR reaches a stable, passing state.

@Jagadeeshftw

[precious-akpan]

@Jagadeeshftw awaiting your review

[precious-akpan]

@Jagadeeshftw Please review this PR when you have a chance. All tests are passing and the implementation is complete. Ready for merge.