Add a test-oriented strict preset

[sethlivingston]

Summary

Add a test-friendly preset alongside the current strict preset so test code can stay readable without fighting ceremony-heavy rules intended for production/library code.

Context

While integrating @sethlivingston/eslint-plugin-typescript-narrows into oneway-http, the current strict preset worked well for library code but pushed test files toward extra ceremony with limited payoff.

The main pain points were:

• @typescript-eslint/prefer-readonly-parameter-types
• @typescript-eslint/explicit-function-return-type
• possibly @typescript-eslint/require-await depending on the intended opinion for tests

Proposal

Add a new preset, for example:

• configs.test
• or configs.strictTest

This preset should start from the current strict base and relax rules that create friction in Vitest/Jest-style test code.

Acceptance criteria

• A documented test-oriented preset exists.
• It is intended for **/*.test.ts, **/*.spec.ts, and related helper files.
• It relaxes the most ceremony-heavy rules for tests while keeping the important safety/value rules.
• The README shows how to compose the strict preset for source files and the test preset for test files.

[sethlivingston]

Closing as resolved.