Use shared Renovate preset and update pnpm to v10

[bdrhn9]

As a part of https://github.com/api3dao/tasks/issues/1855
Closes #14

Changes beyond the task description

• Added ethers@^5.7.2 as a direct devDependency: pnpm's strict module resolution means peer dependencies must be explicit. The v5 hardhat tooling (@nomiclabs/hardhat-ethers, @nomicfoundation/hardhat-chai-matchers, etc.) requires ethers v5 as a peer, which was previously satisfied implicitly via yarn's flat hoisting.
• Explicit prettier-plugin-solidity in .prettierrc.js: pnpm does not auto-discover prettier plugins from hoisted transitive dependencies. Added plugins: ['prettier-plugin-solidity'] to make the Solidity parser available.
• Fixed BigNumber comparison in test: lockfile regeneration resolved hardhat@^2.24.3 to 2.28.4, which changed hardhat/common/bigInt#isBigNumber to only recognize native BigInt (not ethers v5 BigNumber). Updated test/DataFeedReaderExample.sol.js to use .toString() comparison.
• Added @nodary/* to Renovate and minimumReleaseAgeExclude: treats nodary packages the same as @api3/*
• Updated CI workflow: replaced yarn with pnpm/action-setup@v4, single lint-build-test job, bumped to actions/checkout@v6, actions/setup-node@v6, and Node 20.

Test plan

• CI workflow runs successfully after push

[hiletmis]

LGTM

Just a reminder README.md contains outdated yarn instructions