Audit all types for whether they need `readonly` modifier

Description

Contributor guide

Tech stack

typescript

Domain

developer experience

Issue type

refactor

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-2 days

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

blocked

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

TypeScriptfamiliarity with type festreadonly modifier understanding

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

50

Research direction

First, review the changes made in the similar issue #758 to understand the pattern. Then, examine all type definitions in the type fest source (likely in the 'source' directory) to identify types where a `readonly` modifier is missing but could be applied, especially for object types and arrays. Pay attention to utility types that wrap or transform objects, as they may need to preserve or add readonly constraints. Check the GitHub issue comments for any guidance from maintainers or the assignee (@Emiyaaaaa).