Add oxlint config and custom expect-expect JS plugin for bun:test

[rhuanbarreto]

Problem

Tests with no expect() calls silently pass, giving false confidence. The standard jest/expect-expect rule exists in oxlint but its Rust implementation only recognizes jest and vitest imports — it silently ignores bun:test.

We also have no .oxlintrc.json config file — the lint script runs bare oxlint --deny-warnings . with implicit defaults.

Proposal

1. Add .oxlintrc.json — explicit config instead of relying on defaults
2. Write a custom JS plugin (lint/expect-expect.ts) using oxlint's JS plugins API that implements expect-expect for bun:test
3. Register it via jsPlugins in .oxlintrc.json

The rule should flag any test() or test.skipIf(...)() call whose body contains no expect() call.

Context

Discovered during test cleanup in #352 — several tests were passing with zero assertions (early return instead of test.skipIf, empty callback bodies, tautological assertions). The lack of a lint rule meant these accumulated silently over time.

oxlint JS plugins support TypeScript natively in Bun, so the plugin can be a .ts file with no build step.

References

• oxlint JS plugins docs: https://oxc.rs/docs/guide/usage/linter/js-plugins.html
• PR that surfaced this: fix(ci): resolve macOS and Windows test failures in release builds #352