deps: update dependencies - #194

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: 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/

src/internal/parser.ts:518:33: Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator.

src/cli/parseSimple.ts:8:9: Unnecessary conditional, value is always truthy.

src/cli/parse.ts:8:9: Unnecessary conditional, value is always truthy.

src/internal/core/index.ts:265:8: This condition will always return the same value since the types have no overlap.

vitest.config.ts:8:8: Forbidden non-null assertion.