feat(refund_ratio_helper): ticker fallbacks, DB precision rows, CSV export, rate limit - #591

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

'addr' is assigned a value but never used. Allowed unused vars must match /^_/u

'insertEvent' is defined but never used. Allowed unused vars must match /^_/u

'Response' is defined but never used. Allowed unused vars must match /^_/u

'Request' is defined but never used. Allowed unused vars must match /^_/u

'TEST_API_KEY' is defined but never used. Allowed unused vars must match /^_/u

'TEST_API_KEY' is defined but never used. Allowed unused vars must match /^_/u

'TEST_API_KEY' is defined but never used. Allowed unused vars must match /^_/u

'method' is assigned a value but never used. Allowed unused vars must match /^_/u

'sourceAddress' is assigned a value but never used. Allowed unused vars must match /^_/u

'KNOWN_ASSETS' is defined but never used. Allowed unused vars must match /^_/u