Swap ESLint for Biome, mirroring yearn.fi lint setup

[rossgalloway]

TODO

• Summary: Replace ESLint with Biome and mirror the lint/format setup used in ../yearn.fi
• Location: tooling (package.json, lint config files)
• Group: dev-tooling
• Branch: root: master, work: tooling-updates
• Spec: embedded below

Spec

• Context: We want this repo to align with the linting stack and rules already standardized in ../yearn.fi.
• Goals:
  • Remove ESLint from the toolchain.
  • Add Biome with the same rule configuration and scripts as ../yearn.fi.
  • Keep lint/format commands consistent for contributors and CI.
• Non-goals:
  • Broad refactors or code-style changes beyond what Biome enforces.
• Proposed implementation (files):
  • package.json (scripts, devDependencies)
  • Biome config file(s) matching ../yearn.fi
  • Remove ESLint config files (.eslintrc*, .eslintignore) if present
  • Update docs/README if lint commands are documented
• Acceptance criteria:
  • bun run lint uses Biome and passes.
  • bun run format uses Biome and passes.
  • ESLint dependencies/config files are removed.
  • Linting rules match ../yearn.fi.
• Manual QA steps:
  • Run bun run lint and bun run format.
  • Verify CI (if any) uses the new scripts.

Status: In progress (2026-01-08)
Assigned: @me
Branch: tooling-updates