Refactor: Centralize duplicated configuration across query scripts

[Copilot]

Four scripts (query-token-balance.{js,py,sh} and fetch-example.js) each hardcoded identical configuration values: API base URL, default address, chain ID, pagination, module/action, and address validation pattern.

Changes

• Centralized config: Extended etherscan-config.json with address_validation_pattern, made it single source of truth for all scripts
• Error handling: Added descriptive errors for missing/malformed config in all implementations
• Performance: Shell script parses JSON once (previously 8x in python3 fallback), Python compiles regex at module level (previously per-call)

Example

Before (duplicated in each script):

const baseUrl = 'https://api.etherscan.io/v2/api';
const defaultAddress = '0x983e3660c0bE01991785F80f266A84B911ab59b0';
const chainId = 1;

After (all scripts):

const config = JSON.parse(fs.readFileSync('etherscan-config.json', 'utf8'));
const baseUrl = config.etherscan_api.base_url;
const defaultAddress = config.etherscan_api.example_address;

Configuration changes now require updating one file instead of four.

Stats: 5 files changed (+125/-38), zero duplication remaining

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.etherscan.io
  • Triggering command: /usr/local/bin/node node fetch-example.js (dns block)
  • Triggering command: /usr/bin/curl curl -s REDACTED (dns block)
  • Triggering command: /usr/local/bin/node node -e require('./fetch-example.js') (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Find and refactor duplicated code.

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