Replace instanceof checks with Effect guards - #5

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

packages/effect-branded-id/test/branded-id.test.ts:32:52: Require a message for "toThrow".

packages/effect-branded-id/test/branded-id.test.ts:31:39: Require a message for "toThrow".

packages/effect-branded-id/test/branded-id.test.ts:30:37: Require a message for "toThrow".

packages/effect-branded-id/test/branded-id.test.ts:29:34: Require a message for "toThrow".

packages/fold-agent/test/Mode/Subagents.vi.test.ts:99:3: Unexpected conditional expect

packages/fold-agent/test/Mode/Subagents.vi.test.ts:93:3: Expect takes at most 1 argument

packages/fold-tui-theme/src/github/stats.ts:65:18: Do not use `new Array(singleArgument)`.

packages/fold-agent/test/Config/ConfigProfiles.vi.test.ts:138:5: Expect takes at most 1 argument

packages/fold-agent/test/Config/ConfigProfiles.vi.test.ts:133:5: Expect takes at most 1 argument