Switch to pnpm and Node.js 24

[carlos-poly]

Summary

• Switch package manager from Yarn to pnpm (lockfile, CI workflow, Makefile, README)
• Bump minimum Node version from 20.10 to 24
• Remove ethers from dependencies (never imported anywhere)
• Move @ethersproject/providers and @ethersproject/wallet to devDependencies (source only uses type imports)
• Remove 8 unused devDependencies: eslint-config-standard-with-typescript, eslint-plugin-import, eslint-plugin-n, eslint-plugin-node, eslint-plugin-promise, esm, ts-mocha, ts-node
• Drop unused --require tsconfig-paths/register from test command

Validation

• pnpm build succeeds
• All 22 tests pass
• CI workflow updated to install pnpm and use pnpm commands
• Verify CI passes on this branch

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Note

Medium Risk
Moderate risk because it changes the package manager and bumps the required Node version to 24, which can affect dependency resolution and CI/runtime compatibility. No application logic changes, but lockfile/tooling shifts may surface build/test differences.

Overview
Migrates build/test/lint workflows from Yarn to pnpm: GitHub Actions now installs pnpm (pnpm/action-setup@v4) and runs pnpm install/lint/build/test, and the Makefile test target switches to pnpm nyc.

Updates package metadata for the new toolchain: package.json bumps version to 3.1.0, sets engines to node >=24 and pnpm >=10, and reclassifies some packages between dependencies and devDependencies. Adds pnpm-lock.yaml and removes Yarn-specific ignores/docs references.

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[carlos-poly]

• Add WalletClient support to ExchangeOrderBuilder #20
• Switch to pnpm and Node.js 24 #19 👈 (View in Graphite)
• main

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